Intro to the TSConfig Reference

A TSConfig file in a directory indicates that the directory is the root of a TypeScript or JavaScript project...

Compiler Options

"compilerOptions"

JavaScript Support
  1. allowJs,
  2. checkJs and
  3. maxNodeModuleJsDepth
Editor Support
  1. disableSizeLimit and
  2. plugins
Command Line

    Root Fields

    Starting up are the root options in the TSConfig - these options relate to how your TypeScript or JavaScript project is set up.

    # Files - files

    Specifies an allowlist of files to include in the program. An error occurs if any of the files can’t be found.

    {
    "": [
    "core.ts",
    "sys.ts",
    "types.ts",
    "scanner.ts",
    "parser.ts",
    "utilities.ts",
    "binder.ts",
    "checker.ts",
    "tsc.ts"
    ]
    }

    This is useful when you only have a small number of files and don’t need to use a glob to reference many files. If you need that then use include.

    # Extends - extends

    The value of extends is a string which contains a path to another configuration file to inherit from. The path may use Node.js style resolution.

    The configuration from the base file are loaded first, then overridden by those in the inheriting config file. All relative paths found in the configuration file will be resolved relative to the configuration file they originated in.

    It’s worth noting that files, include and exclude from the inheriting config file overwrite those from the base config file, and that circularity between configuration files is not allowed.

    Currently, the only top-level property that is excluded from inheritance is references.

    Example

    configs/base.json:

    tsconfig.json:

    {
    "": "./configs/base",
    "": ["main.ts", "supplemental.ts"]
    }

    tsconfig.nostrictnull.json:

    {
    "": "./tsconfig",
    }
    }

    Properties with relative paths found in the configuration file, which aren’t excluded from inheritance, will be resolved relative to the configuration file they originated in.

    • Default:

      false

    • Released:

      2.1

    # Include - include

    Specifies an array of filenames or patterns to include in the program. These filenames are resolved relative to the directory containing the tsconfig.json file.

    json
    {
    "include": ["src/**/*", "tests/**/*"]
    }

    Which would include:

    . ├── scripts ⨯ │ ├── lint.ts ⨯ │ ├── update_deps.ts ⨯ │ └── utils.ts ⨯ ├── src ✓ │ ├── client ✓ │ │ ├── index.ts ✓ │ │ └── utils.ts ✓ │ ├── server ✓ │ │ └── index.ts ✓ ├── tests ✓ │ ├── app.test.ts ✓ │ ├── utils.ts ✓ │ └── tests.d.ts ✓ ├── package.json ├── tsconfig.json └── yarn.lock

    include and exclude support wildcard characters to make glob patterns:

    • * matches zero or more characters (excluding directory separators)
    • ? matches any one character (excluding directory separators)
    • **/ matches any directory nested to any level

    If a glob pattern doesn’t include a file extension, then only files with supported extensions are included (e.g. .ts, .tsx, and .d.ts by default, with .js and .jsx if allowJs is set to true).

    # Exclude - exclude

    Specifies an array of filenames or patterns that should be skipped when resolving include.

    Important: exclude only changes which files are included as a result of the include setting. A file specified by exclude can still become part of your codebase due to an import statement in your code, a types inclusion, a /// <reference directive, or being specified in the files list.

    It is not a mechanism that prevents a file from being included in the codebase - it simply changes what the include setting finds.

    # References - references

    Project references are a way to structure your TypeScript programs into smaller pieces. Using Project References can greatly improve build and editor interaction times, enforce logical separation between components, and organize your code in new and improved ways.

    You can read more about how references works in the Project References section of the handbook

    • Default:

      false

    Compiler Options

    These options make up the bulk of TypeScript’s configuration and it covers how the language should work.

    #Type Checking

    # Allow Unreachable Code - allowUnreachableCode

    When:

    • undefined (default) provide suggestions as warnings to editors
    • true unreachable code is ignored
    • false raises compiler errors about unreachable code

    These warnings are only about code which is provably unreachable due to the use of JavaScript syntax, for example:

    ts
    function fn(n: number) {
    if (n > 5) {
    return true;
    } else {
    return false;
    }
    return true;
    }

    With "allowUnreachableCode": false:

    ts
    function fn(n: number) {
    if (n > 5) {
    return true;
    } else {
    return false;
    }
    return true;
    Unreachable code detected.7027Unreachable code detected.
    }
    Try

    This does not affect errors on the basis of code which appears to be unreachable due to type analysis.

    • Default:

      undefined

    • Released:

      1.8

    # Allow Unused Labels - allowUnusedLabels

    When:

    • undefined (default) provide suggestions as warnings to editors
    • true unused labels are ignored
    • false raises compiler errors about unused labels

    Labels are very rare in JavaScript and typically indicate an attempt to write an object literal:

    ts
    function verifyAge(age: number) {
    // Forgot 'return' statement
    if (age > 18) {
    verified: true;
    Unused label.7028Unused label.
    }
    }
    Try
    • Default:

      undefined

    • Released:

      1.8

    # Always Strict - alwaysStrict

    Ensures that your files are parsed in the ECMAScript strict mode, and emit “use strict” for each source file.

    ECMAScript strict mode was introduced in ES5 and provides behavior tweaks to the runtime of the JavaScript engine to improve performance, and makes a set of errors throw instead of silently ignoring them.

    • Recommended
    • Default:
      • true if strict,

      • false otherwise.

    • Related:
    • Released:

      2.1

    # exactOptionalPropertyTypes - exactOptionalPropertyTypes

    With exactOptionalPropertyTypes enabled, TypeScript applies stricter rules around how it handles properties on type or interfaces which have a ? prefix.

    For example, this interface declares that there is a property which can be one of two strings: ‘dark’ or ‘light’ or it should not be in the object.

    ts
    interface UserDefaults {
    // The absence of a value represents 'system'
    colorThemeOverride?: "dark" | "light";
    }

    Without this flag enabled, there are three values which you can set colorThemeOverride to be: “dark”, “light” and undefined.

    Setting the value to undefined will allow most JavaScript runtime checks for the existence to fail, which is effectively falsy. However, this isn’t quite accurate colorThemeOverride: undefined is not the same as colorThemeOverride not being defined. For example "colorThemeOverride" in settings would have different behavior with undefined as the key compared to not being defined.

    exactOptionalPropertyTypes makes TypeScript truly enforce the definition provided as an optional property:

    ts
    const settings = getUserSettings();
    settings.colorThemeOverride = "dark";
    settings.colorThemeOverride = "light";
     
    // But not:
    settings.colorThemeOverride = undefined;
    Type 'undefined' is not assignable to type '"dark" | "light"' with 'exactOptionalPropertyTypes: true'. Consider adding 'undefined' to the type of the target.2412Type 'undefined' is not assignable to type '"dark" | "light"' with 'exactOptionalPropertyTypes: true'. Consider adding 'undefined' to the type of the target.
    Try
    • Recommended
    • Default:

      false

    • Released:

      4.4

    # No Fallthrough Cases In Switch - noFallthroughCasesInSwitch

    Report errors for fallthrough cases in switch statements. Ensures that any non-empty case inside a switch statement includes either break or return. This means you won’t accidentally ship a case fallthrough bug.

    ts
    const a: number = 6;
     
    switch (a) {
    case 0:
    Fallthrough case in switch.7029Fallthrough case in switch.
    console.log("even");
    case 1:
    console.log("odd");
    break;
    }
    Try
    • Default:

      false

    • Released:

      1.8

    # No Implicit Any - noImplicitAny

    In some cases where no type annotations are present, TypeScript will fall back to a type of any for a variable when it cannot infer the type.

    This can cause some errors to be missed, for example:

    ts
    function fn(s) {
    // No error?
    console.log(s.subtr(3));
    }
    fn(42);
    Try

    Turning on noImplicitAny however TypeScript will issue an error whenever it would have inferred any:

    ts
    function fn(s) {
    Parameter 's' implicitly has an 'any' type.7006Parameter 's' implicitly has an 'any' type.
    console.log(s.subtr(3));
    }
    Try
    • Recommended
    • Default:
      • true if strict,

      • false otherwise.

    • Related:

    # noImplicitOverride - noImplicitOverride

    When working with classes which use inheritance, it’s possible for a sub-class to get “out of sync” with the functions it overloads when they are renamed in the base class.

    For example, imagine you are modeling a music album syncing system:

    ts
    class Album {
    download() {
    // Default behavior
    }
    }
     
    class SharedAlbum extends Album {
    download() {
    // Override to get info from many sources
    }
    }
    Try

    Then when you add support for machine-learning generated playlists, you refactor the Album class to have a ‘setup’ function instead:

    ts
    class Album {
    setup() {
    // Default behavior
    }
    }
     
    class MLAlbum extends Album {
    setup() {
    // Override to get info from algorithm
    }
    }
     
    class SharedAlbum extends Album {
    download() {
    // Override to get info from many sources
    }
    }
    Try

    In this case, TypeScript has provided no warning that download on SharedAlbum expected to override a function in the base class.

    Using noImplicitOverride you can ensure that the sub-classes never go out of sync, by ensuring that functions which override include the keyword override.

    The following example has noImplicitOverride enabled, and you can see the error received when override is missing:

    ts
    class Album {
    setup() {}
    }
     
    class MLAlbum extends Album {
    override setup() {}
    }
     
    class SharedAlbum extends Album {
    setup() {}
    This member must have an 'override' modifier because it overrides a member in the base class 'Album'.4114This member must have an 'override' modifier because it overrides a member in the base class 'Album'.
    }
    Try
    • Default:

      false

    • Released:

      4.3

    # No Implicit Returns - noImplicitReturns

    When enabled, TypeScript will check all code paths in a function to ensure they return a value.

    ts
    function lookupHeadphonesManufacturer(color: "blue" | "black"): string {
    Function lacks ending return statement and return type does not include 'undefined'.2366Function lacks ending return statement and return type does not include 'undefined'.
    if (color === "blue") {
    return "beats";
    } else {
    "bose";
    }
    }
    Try
    • Default:

      false

    • Released:

      1.8

    # No Implicit This - noImplicitThis

    Raise error on ‘this’ expressions with an implied ‘any’ type.

    For example, the class below returns a function which tries to access this.width and this.height – but the context for this inside the function inside getAreaFunction is not the instance of the Rectangle.

    ts
    class Rectangle {
    width: number;
    height: number;
     
    constructor(width: number, height: number) {
    this.width = width;
    this.height = height;
    }
     
    getAreaFunction() {
    return function () {
    return this.width * this.height;
    'this' implicitly has type 'any' because it does not have a type annotation.
    'this' implicitly has type 'any' because it does not have a type annotation.
    2683
    2683
    'this' implicitly has type 'any' because it does not have a type annotation.
    'this' implicitly has type 'any' because it does not have a type annotation.
    };
    }
    }
    Try
    • Recommended
    • Default:
      • true if strict,

      • false otherwise.

    • Related:
    • Released:

      2.0

    # noPropertyAccessFromIndexSignature - noPropertyAccessFromIndexSignature

    This setting ensures consistency between accessing a field via the “dot” (obj.key) syntax, and “indexed” (obj["key"]) and the way which the property is declared in the type.

    Without this flag, TypeScript will allow you to use the dot syntax to access fields which are not defined:

    ts
    interface GameSettings {
    // Known up-front properties
    speed: "fast" | "medium" | "slow";
    quality: "high" | "low";
     
    // Assume anything unknown to the interface
    // is a string.
    [key: string]: string;
    }
     
    const settings = getSettings();
    settings.speed;
    (property) GameSettings.speed: "fast" | "medium" | "slow"
    settings.quality;
    (property) GameSettings.quality: "high" | "low"
     
    // Unknown key accessors are allowed on
    // this object, and are `string`
    settings.username;
    string
    Try

    Turning the flag on will raise an error because the unknown field uses dot syntax instead of indexed syntax.

    ts
    const settings = getSettings();
    settings.speed;
    settings.quality;
     
    // This would need to be settings["username"];
    settings.username;
    Property 'username' comes from an index signature, so it must be accessed with ['username'].4111Property 'username' comes from an index signature, so it must be accessed with ['username'].
    string
    Try

    The goal of this flag is to signal intent in your calling syntax about how certain you are this property exists.

    • Default:

      false

    • Released:

      4.2

    # noUncheckedIndexedAccess - noUncheckedIndexedAccess

    TypeScript has a way to describe objects which have unknown keys but known values on an object, via index signatures.

    ts
    interface EnvironmentVars {
    NAME: string;
    OS: string;
     
    // Unknown properties are covered by this index signature.
    [propName: string]: string;
    }
     
    declare const env: EnvironmentVars;
     
    // Declared as existing
    const sysName = env.NAME;
    const os = env.OS;
    const os: string
     
    // Not declared, but because of the index
    // signature, then it is considered a string
    const nodeEnv = env.NODE_ENV;
    const nodeEnv: string
    Try

    Turning on noUncheckedIndexedAccess will add undefined to any un-declared field in the type.

    ts
    declare const env: EnvironmentVars;
     
    // Declared as existing
    const sysName = env.NAME;
    const os = env.OS;
    const os: string
     
    // Not declared, but because of the index
    // signature, then it is considered a string
    const nodeEnv = env.NODE_ENV;
    const nodeEnv: string | undefined
    Try
    • Default:

      false

    • Released:

      4.1

    # No Unused Locals - noUnusedLocals

    Report errors on unused local variables.

    ts
    const createKeyboard = (modelID: number) => {
    const defaultModelID = 23;
    'defaultModelID' is declared but its value is never read.6133'defaultModelID' is declared but its value is never read.
    return { type: "keyboard", modelID };
    };
    Try
    • Default:

      false

    • Released:

      2.0

    # No Unused Parameters - noUnusedParameters

    Report errors on unused parameters in functions.

    ts
    const createDefaultKeyboard = (modelID: number) => {
    'modelID' is declared but its value is never read.6133'modelID' is declared but its value is never read.
    const defaultModelID = 23;
    return { type: "keyboard", modelID: defaultModelID };
    };
    Try
    • Default:

      false

    • Released:

      2.0

    # Strict - strict

    The strict flag enables a wide range of type checking behavior that results in stronger guarantees of program correctness. Turning this on is equivalent to enabling all of the strict mode family options, which are outlined below. You can then turn off individual strict mode family checks as needed.

    Future versions of TypeScript may introduce additional stricter checking under this flag, so upgrades of TypeScript might result in new type errors in your program. When appropriate and possible, a corresponding flag will be added to disable that behavior.

    # Strict Bind Call Apply - strictBindCallApply

    When set, TypeScript will check that the built-in methods of functions call, bind, and apply are invoked with correct argument for the underlying function:

    ts
    // With strictBindCallApply on
    function fn(x: string) {
    return parseInt(x);
    }
     
    const n1 = fn.call(undefined, "10");
     
    const n2 = fn.call(undefined, false);
    Argument of type 'boolean' is not assignable to parameter of type 'string'.2345Argument of type 'boolean' is not assignable to parameter of type 'string'.
    Try

    Otherwise, these functions accept any arguments and will return any:

    ts
    // With strictBindCallApply off
    function fn(x: string) {
    return parseInt(x);
    }
     
    // Note: No error; return type is 'any'
    const n = fn.call(undefined, false);
    Try
    • Recommended
    • Default:
      • true if strict,

      • false otherwise.

    • Related:
    • Released:

      3.2

    # Strict Function Types - strictFunctionTypes

    When enabled, this flag causes functions parameters to be checked more correctly.

    Here’s a basic example with strictFunctionTypes off:

    ts
    function fn(x: string) {
    console.log("Hello, " + x.toLowerCase());
    }
     
    type StringOrNumberFunc = (ns: string | number) => void;
     
    // Unsafe assignment
    let func: StringOrNumberFunc = fn;
    // Unsafe call - will crash
    func(10);
    Try

    With strictFunctionTypes on, the error is correctly detected:

    ts
    function fn(x: string) {
    console.log("Hello, " + x.toLowerCase());
    }
     
    type StringOrNumberFunc = (ns: string | number) => void;
     
    // Unsafe assignment is prevented
    let func: StringOrNumberFunc = fn;
    Type '(x: string) => void' is not assignable to type 'StringOrNumberFunc'. Types of parameters 'x' and 'ns' are incompatible. Type 'string | number' is not assignable to type 'string'. Type 'number' is not assignable to type 'string'.2322Type '(x: string) => void' is not assignable to type 'StringOrNumberFunc'. Types of parameters 'x' and 'ns' are incompatible. Type 'string | number' is not assignable to type 'string'. Type 'number' is not assignable to type 'string'.
    Try

    During development of this feature, we discovered a large number of inherently unsafe class hierarchies, including some in the DOM. Because of this, the setting only applies to functions written in function syntax, not to those in method syntax:

    ts
    type Methodish = {
    func(x: string | number): void;
    };
     
    function fn(x: string) {
    console.log("Hello, " + x.toLowerCase());
    }
     
    // Ultimately an unsafe assignment, but not detected
    const m: Methodish = {
    func: fn,
    };
    m.func(10);
    Try
    • Recommended
    • Default:
      • true if strict,

      • false otherwise.

    • Related:
    • Released:

      2.6

    # Strict Null Checks - strictNullChecks

    When strictNullChecks is false, null and undefined are effectively ignored by the language. This can lead to unexpected errors at runtime.

    When strictNullChecks is true, null and undefined have their own distinct types and you’ll get a type error if you try to use them where a concrete value is expected.

    For example with this TypeScript code, users.find has no guarantee that it will actually find a user, but you can write code as though it will:

    ts
    declare const loggedInUsername: string;
     
    const users = [
    { name: "Oby", age: 12 },
    { name: "Heera", age: 32 },
    ];
     
    const loggedInUser = users.find((u) => u.name === loggedInUsername);
    console.log(loggedInUser.age);
    Try

    Setting strictNullChecks to true will raise an error that you have not made a guarantee that the loggedInUser exists before trying to use it.

    ts
    declare const loggedInUsername: string;
     
    const users = [
    { name: "Oby", age: 12 },
    { name: "Heera", age: 32 },
    ];
     
    const loggedInUser = users.find((u) => u.name === loggedInUsername);
    console.log(loggedInUser.age);
    Object is possibly 'undefined'.2532Object is possibly 'undefined'.
    Try

    The second example failed because the array’s find function looks a bit like this simplification:

    ts
    // When strictNullChecks: true
    type Array = {
    find(predicate: (value: any, index: number) => boolean): S | undefined;
    };
    // When strictNullChecks: false the undefined is removed from the type system,
    // allowing you to write code which assumes it always found a result
    type Array = {
    find(predicate: (value: any, index: number) => boolean): S;
    };
    • Recommended
    • Default:
      • true if strict,

      • false otherwise.

    • Related:
    • Released:

      2.0

    # Strict Property Initialization - strictPropertyInitialization

    When set to true, TypeScript will raise an error when a class property was declared but not set in the constructor.

    ts
    class UserAccount {
    name: string;
    accountType = "user";
     
    email: string;
    Property 'email' has no initializer and is not definitely assigned in the constructor.2564Property 'email' has no initializer and is not definitely assigned in the constructor.
    address: string | undefined;
     
    constructor(name: string) {
    this.name = name;
    // Note that this.email is not set
    }
    }
    Try

    In the above case:

    • this.name is set specifically.
    • this.accountType is set by default.
    • this.email is not set and raises an error.
    • this.address is declared as potentially undefined which means it does not have to be set.
    • Recommended
    • Default:
      • true if strict,

      • false otherwise.

    • Related:
    • Released:

      2.7

    # useUnknownInCatchVariables - useUnknownInCatchVariables

    In TypeScript 4.0, support was added to allow changing the type of the variable in a catch clause from any to unknown. Allowing for code like:

    ts
    try {
    // ...
    } catch (err) {
    // We have to verify err is an
    // error before using it as one.
    if (err instanceof Error) {
    console.log(err.message);
    }
    }
    Try

    This pattern ensures that error handling code becomes more comprehensive because you cannot guarantee that the object being thrown is a Error subclass ahead of time. With the flag useUnknownInCatchVariables enabled, then you do not need the additional syntax (: unknown) nor a linter rule to try enforce this behavior.

    #Modules

    # Allow Umd Global Access - allowUmdGlobalAccess

    When set to true, allowUmdGlobalAccess lets you access UMD exports as globals from inside module files. A module file is a file that has imports and/or exports. Without this flag, using an export from a UMD module requires an import declaration.

    An example use case for this flag would be a web project where you know the particular library (like jQuery or Lodash) will always be available at runtime, but you can’t access it with an import.

    • Default:

      false

    • Released:

      3.5

    # Base Url - baseUrl

    Lets you set a base directory to resolve non-absolute module names.

    You can define a root folder where you can do absolute file resolution. E.g.

    baseUrl ├── ex.ts ├── hello │ └── world.ts └── tsconfig.json

    With "baseUrl": "./" inside this project TypeScript will look for files starting at the same folder as the tsconfig.json.

    ts
    import { helloWorld } from "hello/world";
    console.log(helloWorld);

    If you get tired of imports always looking like "../" or "./", or needing to change them as you move files, this is a great way to fix that.

      # Module - module

      Sets the module system for the program. See the Modules reference page for more information. You very likely want "CommonJS" for node projects.

      Changing module affects moduleResolution which also has a reference page.

      Here’s some example output for this file:

      ts
      // @filename: index.ts
      import { valueOfPi } from "./constants";
       
      export const twoPi = valueOfPi * 2;
      Try

      CommonJS

      ts
      "use strict";
      Object.defineProperty(exports, "__esModule", { value: true });
      exports.twoPi = void 0;
      const constants_1 = require("./constants");
      exports.twoPi = constants_1.valueOfPi * 2;
       
      Try

      UMD

      ts
      (function (factory) {
      if (typeof module === "object" && typeof module.exports === "object") {
      var v = factory(require, exports);
      if (v !== undefined) module.exports = v;
      }
      else if (typeof define === "function" && define.amd) {
      define(["require", "exports", "./constants"], factory);
      }
      })(function (require, exports) {
      "use strict";
      Object.defineProperty(exports, "__esModule", { value: true });
      exports.twoPi = void 0;
      const constants_1 = require("./constants");
      exports.twoPi = constants_1.valueOfPi * 2;
      });
       
      Try

      AMD

      ts
      define(["require", "exports", "./constants"], function (require, exports, constants_1) {
      "use strict";
      Object.defineProperty(exports, "__esModule", { value: true });
      exports.twoPi = void 0;
      exports.twoPi = constants_1.valueOfPi * 2;
      });
       
      Try

      System

      ts
      System.register(["./constants"], function (exports_1, context_1) {
      "use strict";
      var constants_1, twoPi;
      var __moduleName = context_1 && context_1.id;
      return {
      setters: [
      function (constants_1_1) {
      constants_1 = constants_1_1;
      }
      ],
      execute: function () {
      exports_1("twoPi", twoPi = constants_1.valueOfPi * 2);
      }
      };
      });
       
      Try

      ESNext

      ts
      import { valueOfPi } from "./constants";
      export const twoPi = valueOfPi * 2;
       
      Try

      ES2020

      ts
      import { valueOfPi } from "./constants";
      export const twoPi = valueOfPi * 2;
       
      Try

      ES2015/ES6

      ts
      import { valueOfPi } from "./constants";
      export const twoPi = valueOfPi * 2;
       
      Try

      If you are wondering about the difference between ES2015 (aka ES6) and ES2020, ES2020 adds support for dynamic imports, and import.meta.

      node12/nodenext

      ts
      "use strict";
      Object.defineProperty(exports, "__esModule", { value: true });
      exports.twoPi = void 0;
      const constants_js_1 = require("./constants.js");
      exports.twoPi = constants_js_1.valueOfPi * 2;
       
      Try

      Introduced in TypeScript 4.5, node12 and nodenext declare support for Node’s ECMAScript Module Support. The emitted JavaScript is the same as ES2020 which is the same import/export syntax in the TypeScript file. You can learn more in the 4.5 release notes.

      None

      ts
      "use strict";
      Object.defineProperty(exports, "__esModule", { value: true });
      exports.twoPi = void 0;
      const constants_1 = require("./constants");
      exports.twoPi = constants_1.valueOfPi * 2;
       
      Try
      • Default:
        • CommonJS if target is ES3 or ES5,

        • ES6/ES2015 otherwise.

      • Allowed:
        • none

        • commonjs

        • amd

        • umd

        • system

        • es6/es2015

        • es2020

        • es2022

        • esnext

        • node12

        • nodenext

      • Related:
      • Released:

        1.0

      # Module Resolution - moduleResolution

      Specify the module resolution strategy:

      • 'node' for Node.js’ CommonJS implementation
      • 'node12' or 'nodenext' for Node.js’ ECMAScript Module Support from TypeScript 4.5 onwards
      • 'classic' used in TypeScript before the release of 1.6. You probably won’t need to use classic in modern code

      There is a handbook reference page on Module Resolution

      • Default:
        • Classic if module is AMD, UMD, System or ES6/ES2015,

        • Matches if module is node12 or nodenext,

        • Node otherwise.

      • Allowed:
        • classic

        • node

      • Related:

      # No Resolve - noResolve

      By default, TypeScript will examine the initial set of files for import and <reference directives and add these resolved files to your program.

      If noResolve is set, this process doesn’t happen. However, import statements are still checked to see if they resolve to a valid module, so you’ll need to make sure this is satisfied by some other means.

      • Default:

        false

      # Paths - paths

      A series of entries which re-map imports to lookup locations relative to the baseUrl, there is a larger coverage of paths in the handbook.

      paths lets you declare how TypeScript should resolve an import in your require/imports.

      {
      "": ".", // this must be specified if "paths" is specified.
      "": {
      "jquery": ["node_modules/jquery/dist/jquery"] // this mapping is relative to "baseUrl"
      }
      }
      }

      This would allow you to be able to write import "jquery", and get all of the correct typing locally.

      {
      "": "src",
      "": {
      "app/*": ["app/*"],
      "config/*": ["app/_config/*"],
      "environment/*": ["environments/*"],
      "shared/*": ["app/_shared/*"],
      "helpers/*": ["helpers/*"],
      "tests/*": ["tests/*"]
      },
      }

      In this case, you can tell the TypeScript file resolver to support a number of custom prefixes to find code. This pattern can be used to avoid long relative paths within your codebase.

        # Resolve JSON Module - resolveJsonModule

        Allows importing modules with a ‘.json’ extension, which is a common practice in node projects. This includes generating a type for the import based on the static JSON shape.

        TypeScript does not support resolving JSON files by default:

        ts
        // @filename: settings.json
        Cannot find module './settings.json'. Consider using '--resolveJsonModule' to import module with '.json' extension.2732Cannot find module './settings.json'. Consider using '--resolveJsonModule' to import module with '.json' extension.
        {
        "repo": "TypeScript",
        "dry": false,
        "debug": false
        }
        // @filename: index.ts
        import settings from "./settings.json";
         
        settings.debug === true;
        settings.dry === 2;
        Try

        Enabling the option allows importing JSON, and validating the types in that JSON file.

        ts
        // @filename: settings.json
        {
        "repo": "TypeScript",
        "dry": false,
        This condition will always return 'false' since the types 'boolean' and 'number' have no overlap.2367This condition will always return 'false' since the types 'boolean' and 'number' have no overlap.
        "debug": false
        }
        // @filename: index.ts
        import settings from "./settings.json";
         
        settings.debug === true;
        settings.dry === 2;
        Try
        • Default:

          false

        # Root Dir - rootDir

        Default: The longest common path of all non-declaration input files. If composite is set, the default is instead the directory containing the tsconfig.json file.

        When TypeScript compiles files, it keeps the same directory structure in the output directory as exists in the input directory.

        For example, let’s say you have some input files:

        MyProj ├── tsconfig.json ├── core │ ├── a.ts │ ├── b.ts │ ├── sub │ │ ├── c.ts ├── types.d.ts

        The inferred value for rootDir is the longest common path of all non-declaration input files, which in this case is core/.

        If your outDir was dist, TypeScript would write this tree:

        MyProj ├── dist │ ├── a.js │ ├── b.js │ ├── sub │ │ ├── c.js

        However, you may have intended for core to be part of the output directory structure. By setting rootDir: "." in tsconfig.json, TypeScript would write this tree:

        MyProj ├── dist │ ├── core │ │ ├── a.js │ │ ├── b.js │ │ ├── sub │ │ │ ├── c.js

        Importantly, rootDir does not affect which files become part of the compilation. It has no interaction with the include, exclude, or files tsconfig.json settings.

        Note that TypeScript will never write an output file to a directory outside of outDir, and will never skip emitting a file. For this reason, rootDir also enforces that all files which need to be emitted are underneath the rootDir path.

        For example, let’s say you had this tree:

        MyProj ├── tsconfig.json ├── core │ ├── a.ts │ ├── b.ts ├── helpers.ts

        It would be an error to specify rootDir as core and include as * because it creates a file (helpers.ts) that would need to be emitted outside the outDir (i.e. ../helpers.js).

        • Default:

          Computed from the list of input files.

        • Released:

          1.5

        # Root Dirs - rootDirs

        Using rootDirs, you can inform the compiler that there are many “virtual” directories acting as a single root. This allows the compiler to resolve relative module imports within these “virtual” directories, as if they were merged in to one directory.

        For example:

        src └── views └── view1.ts (can import "./template1", "./view2`) └── view2.ts (can import "./template1", "./view1`) generated └── templates └── views └── template1.ts (can import "./view1", "./view2")
        {
        "": ["src/views", "generated/templates/views"]
        }
        }

        This does not affect how TypeScript emits JavaScript, it only emulates the assumption that they will be able to work via those relative paths at runtime.

        rootDirs can be used to provide a separate “type layer” to files that are not TypeScript or JavaScript by providing a home for generated .d.ts files in another folder. This is technique is useful for bundled applications where you use import of files that aren’t necessarily code:

        sh
        src
        └── index.ts
        └── css
        └── main.css
        └── navigation.css
        generated
        └── css
        └── main.css.d.ts
        └── navigation.css.d.ts
        {
        "": ["src", "generated"]
        }
        }

        This technique lets you generate types ahead of time for the non-code source files. Imports then work naturally based off the source file’s location. For example ./src/index.ts can import the file ./src/css/main.css and TypeScript will be aware of the bundler’s behavior for that filetype via the corresponding generated declaration file.

        ts
        // @filename: index.ts
        import { appClass } from "./main.css";
        Try
        • Default:

          Computed from the list of input files.

        • Released:

          2.0

        # Type Roots - typeRoots

        By default all visible@types” packages are included in your compilation. Packages in node_modules/@types of any enclosing folder are considered visible. For example, that means packages within ./node_modules/@types/, ../node_modules/@types/, ../../node_modules/@types/, and so on.

        If typeRoots is specified, only packages under typeRoots will be included. For example:

        {
        "": ["./typings", "./vendor/types"]
        }
        }

        This config file will include all packages under ./typings and ./vendor/types, and no packages from ./node_modules/@types. All paths are relative to the tsconfig.json.

        # Types - types

        By default all visible@types” packages are included in your compilation. Packages in node_modules/@types of any enclosing folder are considered visible. For example, that means packages within ./node_modules/@types/, ../node_modules/@types/, ../../node_modules/@types/, and so on.

        If types is specified, only packages listed will be included in the global scope. For instance:

        {
        "": ["node", "jest", "express"]
        }
        }

        This tsconfig.json file will only include ./node_modules/@types/node, ./node_modules/@types/jest and ./node_modules/@types/express. Other packages under node_modules/@types/* will not be included.

        What does this affect?

        This option does not affect how @types/* are included in your application code, for example if you had the above compilerOptions example with code like:

        ts
        import * as moment from "moment";
        moment().format("MMMM Do YYYY, h:mm:ss a");

        The moment import would be fully typed.

        When you have this option set, by not including a module in the types array it:

        • Will not add globals to your project (e.g process in node, or expect in Jest)
        • Will not have exports appear as auto-import recommendations

        This feature differs from typeRoots in that it is about specifying only the exact types you want included, whereas typeRoots supports saying you want particular folders.

        #Emit

        # Declaration - declaration

        Generate .d.ts files for every TypeScript or JavaScript file inside your project. These .d.ts files are type definition files which describe the external API of your module. With .d.ts files, tools like TypeScript can provide intellisense and accurate types for un-typed code.

        When declaration is set to true, running the compiler with this TypeScript code:

        ts
        export let helloWorld = "hi";
        Try

        Will generate an index.js file like this:

        ts
        export let helloWorld = "hi";
         
        Try

        With a corresponding helloWorld.d.ts:

        ts
        export declare let helloWorld: string;
         
        Try

        When working with .d.ts files for JavaScript files you may want to use emitDeclarationOnly or use outDir to ensure that the JavaScript files are not overwritten.

        # Declaration Dir - declarationDir

        Offers a way to configure the root directory for where declaration files are emitted.

        example ├── index.ts ├── package.json └── tsconfig.json

        with this tsconfig.json:

        {
        "": true,
        "": "./types"
        }
        }

        Would place the d.ts for the index.ts in a types folder:

        example ├── index.js ├── index.ts ├── package.json ├── tsconfig.json └── types └── index.d.ts

        # Declaration Map - declarationMap

        Generates a source map for .d.ts files which map back to the original .ts source file. This will allow editors such as VS Code to go to the original .ts file when using features like Go to Definition.

        You should strongly consider turning this on if you’re using project references.

        • Default:

          false

        • Released:

          2.9

        # Downlevel Iteration - downlevelIteration

        Downleveling is TypeScript’s term for transpiling to an older version of JavaScript. This flag is to enable support for a more accurate implementation of how modern JavaScript iterates through new concepts in older JavaScript runtimes.

        ECMAScript 6 added several new iteration primitives: the for / of loop (for (el of arr)), Array spread ([a, ...b]), argument spread (fn(...args)), and Symbol.iterator. downlevelIteration allows for these iteration primitives to be used more accurately in ES5 environments if a Symbol.iterator implementation is present.

        Example: Effects on for / of

        With this TypeScript code:

        ts
        const str = "Hello!";
        for (const s of str) {
        console.log(s);
        }
        Try

        Without downlevelIteration enabled, a for / of loop on any object is downleveled to a traditional for loop:

        ts
        "use strict";
        var str = "Hello!";
        for (var _i = 0, str_1 = str; _i < str_1.length; _i++) {
        var s = str_1[_i];
        console.log(s);
        }
         
        Try

        This is often what people expect, but it’s not 100% compliant with ECMAScript iteration protocol. Certain strings, such as emoji (😜), have a .length of 2 (or even more!), but should iterate as 1 unit in a for-of loop. See this blog post by Jonathan New for a longer explanation.

        When downlevelIteration is enabled, TypeScript will use a helper function that checks for a Symbol.iterator implementation (either native or polyfill). If this implementation is missing, you’ll fall back to index-based iteration.

        ts
        "use strict";
        var __values = (this && this.__values) || function(o) {
        var s = typeof Symbol === "function" && Symbol.iterator, m = s && o[s], i = 0;
        if (m) return m.call(o);
        if (o && typeof o.length === "number") return {
        next: function () {
        if (o && i >= o.length) o = void 0;
        return { value: o && o[i++], done: !o };
        }
        };
        throw new TypeError(s ? "Object is not iterable." : "Symbol.iterator is not defined.");
        };
        var e_1, _a;
        var str = "Hello!";
        try {
        for (var str_1 = __values(str), str_1_1 = str_1.next(); !str_1_1.done; str_1_1 = str_1.next()) {
        var s = str_1_1.value;
        console.log(s);
        }
        }
        catch (e_1_1) { e_1 = { error: e_1_1 }; }
        finally {
        try {
        if (str_1_1 && !str_1_1.done && (_a = str_1.return)) _a.call(str_1);
        }
        finally { if (e_1) throw e_1.error; }
        }
         
        Try

        You can use tslib via importHelpers to reduce the amount of inline JavaScript too:

        ts
        "use strict";
        var __values = (this && this.__values) || function(o) {
        var s = typeof Symbol === "function" && Symbol.iterator, m = s && o[s], i = 0;
        if (m) return m.call(o);
        if (o && typeof o.length === "number") return {
        next: function () {
        if (o && i >= o.length) o = void 0;
        return { value: o && o[i++], done: !o };
        }
        };
        throw new TypeError(s ? "Object is not iterable." : "Symbol.iterator is not defined.");
        };
        var e_1, _a;
        var str = "Hello!";
        try {
        for (var str_1 = __values(str), str_1_1 = str_1.next(); !str_1_1.done; str_1_1 = str_1.next()) {
        var s = str_1_1.value;
        console.log(s);
        }
        }
        catch (e_1_1) { e_1 = { error: e_1_1 }; }
        finally {
        try {
        if (str_1_1 && !str_1_1.done && (_a = str_1.return)) _a.call(str_1);
        }
        finally { if (e_1) throw e_1.error; }
        }
         
        Try

        Note: enabling downlevelIteration does not improve compliance if Symbol.iterator is not present in the runtime.

        Example: Effects on Array Spreads

        This is an array spread:

        js
        // Make a new array who elements are 1 followed by the elements of arr2
        const arr = [1, ...arr2];

        Based on the description, it sounds easy to downlevel to ES5:

        js
        // The same, right?
        const arr = [1].concat(arr2);

        However, this is observably different in certain rare cases. For example, if an array has a “hole” in it, the missing index will create an own property if spreaded, but will not if built using concat:

        js
        // Make an array where the '1' element is missing
        let missing = [0, , 1];
        let spreaded = [...missing];
        let concated = [].concat(missing);
        // true
        "1" in spreaded;
        // false
        "1" in concated;

        Just as with for / of, downlevelIteration will use Symbol.iterator (if present) to more accurately emulate ES 6 behavior.

        # Emit BOM - emitBOM

        Controls whether TypeScript will emit a byte order mark (BOM) when writing output files. Some runtime environments require a BOM to correctly interpret a JavaScript files; others require that it is not present. The default value of false is generally best unless you have a reason to change it.

        • Default:

          false

        # Emit Declaration Only - emitDeclarationOnly

        Only emit .d.ts files; do not emit .js files.

        This setting is useful in two cases:

        • You are using a transpiler other than TypeScript to generate your JavaScript.
        • You are using TypeScript to only generate d.ts files for your consumers.

        # Import Helpers - importHelpers

        For certain downleveling operations, TypeScript uses some helper code for operations like extending class, spreading arrays or objects, and async operations. By default, these helpers are inserted into files which use them. This can result in code duplication if the same helper is used in many different modules.

        If the importHelpers flag is on, these helper functions are instead imported from the tslib module. You will need to ensure that the tslib module is able to be imported at runtime. This only affects modules; global script files will not attempt to import modules.

        For example, with this TypeScript:

        ts
        export function fn(arr: number[]) {
        const arr2 = [1, ...arr];
        }

        Turning on downlevelIteration and importHelpers is still false:

        ts
        var __read = (this && this.__read) || function (o, n) {
        var m = typeof Symbol === "function" && o[Symbol.iterator];
        if (!m) return o;
        var i = m.call(o), r, ar = [], e;
        try {
        while ((n === void 0 || n-- > 0) && !(r = i.next()).done) ar.push(r.value);
        }
        catch (error) { e = { error: error }; }
        finally {
        try {
        if (r && !r.done && (m = i["return"])) m.call(i);
        }
        finally { if (e) throw e.error; }
        }
        return ar;
        };
        var __spreadArray = (this && this.__spreadArray) || function (to, from, pack) {
        if (pack || arguments.length === 2) for (var i = 0, l = from.length, ar; i < l; i++) {
        if (ar || !(i in from)) {
        if (!ar) ar = Array.prototype.slice.call(from, 0, i);
        ar[i] = from[i];
        }
        }
        return to.concat(ar || Array.prototype.slice.call(from));
        };
        export function fn(arr) {
        var arr2 = __spreadArray([1], __read(arr), false);
        }
         
        Try

        Then turning on both downlevelIteration and importHelpers:

        ts
        import { __read, __spreadArray } from "tslib";
        export function fn(arr) {
        var arr2 = __spreadArray([1], __read(arr), false);
        }
         
        Try

        You can use noEmitHelpers when you provide your own implementations of these functions.

        # Imports Not Used As Values - importsNotUsedAsValues

        This flag controls how import works, there are 3 different options:

        • remove: The default behavior of dropping import statements which only reference types.

        • preserve: Preserves all import statements whose values or types are never used. This can cause imports/side-effects to be preserved.

        • error: This preserves all imports (the same as the preserve option), but will error when a value import is only used as a type. This might be useful if you want to ensure no values are being accidentally imported, but still make side-effect imports explicit.

        This flag works because you can use import type to explicitly create an import statement which should never be emitted into JavaScript.

        • Allowed:
          • remove

          • preserve

          • error

        • Released:

          3.8

        # Inline Source Map - inlineSourceMap

        When set, instead of writing out a .js.map file to provide source maps, TypeScript will embed the source map content in the .js files. Although this results in larger JS files, it can be convenient in some scenarios. For example, you might want to debug JS files on a webserver that doesn’t allow .map files to be served.

        Mutually exclusive with sourceMap.

        For example, with this TypeScript:

        ts
        const helloWorld = "hi";
        console.log(helloWorld);

        Converts to this JavaScript:

        ts
        "use strict";
        const helloWorld = "hi";
        console.log(helloWorld);
         
        Try

        Then enable building it with inlineSourceMap enabled there is a comment at the bottom of the file which includes a source-map for the file.

        ts
        "use strict";
        const helloWorld = "hi";
        console.log(helloWorld);
        //# sourceMappingURL=data:application/json;base64,eyJ2ZXJzaW9uIjozLCJmaWxlIjoiaW5kZXguanMiLCJzb3VyY2VSb290IjoiIiwic291cmNlcyI6WyJpbmRleC50cyJdLCJuYW1lcyI6W10sIm1hcHBpbmdzIjoiO0FBQUEsTUFBTSxVQUFVLEdBQUcsSUFBSSxDQUFDO0FBQ3hCLE9BQU8sQ0FBQyxHQUFHLENBQUMsVUFBVSxDQUFDLENBQUMifQ==
        Try
        • Default:

          false

        • Released:

          1.5

        # Inline Sources - inlineSources

        When set, TypeScript will include the original content of the .ts file as an embedded string in the source map. This is often useful in the same cases as inlineSourceMap.

        Requires either sourceMap or inlineSourceMap to be set.

        For example, with this TypeScript:

        ts
        const helloWorld = "hi";
        console.log(helloWorld);
        Try

        By default converts to this JavaScript:

        ts
        "use strict";
        const helloWorld = "hi";
        console.log(helloWorld);
         
        Try

        Then enable building it with inlineSources and inlineSourceMap enabled there is a comment at the bottom of the file which includes a source-map for the file. Note that the end is different from the example in inlineSourceMap because the source-map now contains the original source code also.

        ts
        "use strict";
        const helloWorld = "hi";
        console.log(helloWorld);
        //# sourceMappingURL=data:application/json;base64,eyJ2ZXJzaW9uIjozLCJmaWxlIjoiaW5kZXguanMiLCJzb3VyY2VSb290IjoiIiwic291cmNlcyI6WyJpbmRleC50cyJdLCJuYW1lcyI6W10sIm1hcHBpbmdzIjoiO0FBQUEsTUFBTSxVQUFVLEdBQUcsSUFBSSxDQUFDO0FBQ3hCLE9BQU8sQ0FBQyxHQUFHLENBQUMsVUFBVSxDQUFDLENBQUMiLCJzb3VyY2VzQ29udGVudCI6WyJjb25zdCBoZWxsb1dvcmxkID0gXCJoaVwiO1xuY29uc29sZS5sb2coaGVsbG9Xb3JsZCk7Il19
        Try
        • Default:

          false

        • Released:

          1.5

        # Map Root - mapRoot

        Specify the location where debugger should locate map files instead of generated locations. This string is treated verbatim inside the source-map, for example:

        {
        "": true,
        "": "https://my-website.com/debug/sourcemaps/"
        }
        }

        Would declare that index.js will have sourcemaps at https://my-website.com/debug/sourcemaps/index.js.map.

          # New Line - newLine

          Specify the end of line sequence to be used when emitting files: ‘CRLF’ (dos) or ‘LF’ (unix).

          • Default:

            Platform specific.

          • Allowed:
            • crlf

            • lf

          • Released:

            1.5

          # No Emit - noEmit

          Do not emit compiler output files like JavaScript source code, source-maps or declarations.

          This makes room for another tool like Babel, or swc to handle converting the TypeScript file to a file which can run inside a JavaScript environment.

          You can then use TypeScript as a tool for providing editor integration, and as a source code type-checker.

          • Default:

            false

          # No Emit Helpers - noEmitHelpers

          Instead of importing helpers with importHelpers, you can provide implementations in the global scope for the helpers you use and completely turn off emitting of helper functions.

          For example, using this async function in ES5 requires a await-like function and generator-like function to run:

          ts
          const getAPI = async (url: string) => {
          // Get API
          return {};
          };
          Try

          Which creates quite a lot of JavaScript:

          ts
          "use strict";
          var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, P, generator) {
          function adopt(value) { return value instanceof P ? value : new P(function (resolve) { resolve(value); }); }
          return new (P || (P = Promise))(function (resolve, reject) {
          function fulfilled(value) { try { step(generator.next(value)); } catch (e) { reject(e); } }
          function rejected(value) { try { step(generator["throw"](value)); } catch (e) { reject(e); } }
          function step(result) { result.done ? resolve(result.value) : adopt(result.value).then(fulfilled, rejected); }
          step((generator = generator.apply(thisArg, _arguments || [])).next());
          });
          };
          var __generator = (this && this.__generator) || function (thisArg, body) {
          var _ = { label: 0, sent: function() { if (t[0] & 1) throw t[1]; return t[1]; }, trys: [], ops: [] }, f, y, t, g;
          return g = { next: verb(0), "throw": verb(1), "return": verb(2) }, typeof Symbol === "function" && (g[Symbol.iterator] = function() { return this; }), g;
          function verb(n) { return function (v) { return step([n, v]); }; }
          function step(op) {
          if (f) throw new TypeError("Generator is already executing.");
          while (_) try {
          if (f = 1, y && (t = op[0] & 2 ? y["return"] : op[0] ? y["throw"] || ((t = y["return"]) && t.call(y), 0) : y.next) && !(t = t.call(y, op[1])).done) return t;
          if (y = 0, t) op = [op[0] & 2, t.value];
          switch (op[0]) {
          case 0: case 1: t = op; break;
          case 4: _.label++; return { value: op[1], done: false };
          case 5: _.label++; y = op[1]; op = [0]; continue;
          case 7: op = _.ops.pop(); _.trys.pop(); continue;
          default:
          if (!(t = _.trys, t = t.length > 0 && t[t.length - 1]) && (op[0] === 6 || op[0] === 2)) { _ = 0; continue; }
          if (op[0] === 3 && (!t || (op[1] > t[0] && op[1] < t[3]))) { _.label = op[1]; break; }
          if (op[0] === 6 && _.label < t[1]) { _.label = t[1]; t = op; break; }
          if (t && _.label < t[2]) { _.label = t[2]; _.ops.push(op); break; }
          if (t[2]) _.ops.pop();
          _.trys.pop(); continue;
          }
          op = body.call(thisArg, _);
          } catch (e) { op = [6, e]; y = 0; } finally { f = t = 0; }
          if (op[0] & 5) throw op[1]; return { value: op[0] ? op[1] : void 0, done: true };
          }
          };
          var getAPI = function (url) { return __awaiter(void 0, void 0, void 0, function () {
          return __generator(this, function (_a) {
          // Get API
          return [2 /*return*/, {}];
          });
          }); };
           
          Try

          Which can be switched out with your own globals via this flag:

          ts
          "use strict";
          var getAPI = function (url) { return __awaiter(void 0, void 0, void 0, function () {
          return __generator(this, function (_a) {
          // Get API
          return [2 /*return*/, {}];
          });
          }); };
           
          Try

          # No Emit On Error - noEmitOnError

          Do not emit compiler output files like JavaScript source code, source-maps or declarations if any errors were reported.

          This defaults to false, making it easier to work with TypeScript in a watch-like environment where you may want to see results of changes to your code in another environment before making sure all errors are resolved.

          • Default:

            false

          • Released:

            1.4

          # Out Dir - outDir

          If specified, .js (as well as .d.ts, .js.map, etc.) files will be emitted into this directory. The directory structure of the original source files is preserved; see rootDir if the computed root is not what you intended.

          If not specified, .js files will be emitted in the same directory as the .ts files they were generated from:

          sh
          $ tsc
          example
          ├── index.js
          └── index.ts

          With a tsconfig.json like this:

          {
          "": "dist"
          }
          }

          Running tsc with these settings moves the files into the specified dist folder:

          sh
          $ tsc
          example
          ├── dist
          │ └── index.js
          ├── index.ts
          └── tsconfig.json

          # Out File - outFile

          If specified, all global (non-module) files will be concatenated into the single output file specified.

          If module is system or amd, all module files will also be concatenated into this file after all global content.

          Note: outFile cannot be used unless module is None, System, or AMD. This option cannot be used to bundle CommonJS or ES6 modules.

          # Preserve Const Enums - preserveConstEnums

          Do not erase const enum declarations in generated code. const enums provide a way to reduce the overall memory footprint of your application at runtime by emitting the enum value instead of a reference.

          For example with this TypeScript:

          ts
          const enum Album {
          JimmyEatWorldFutures = 1,
          TubRingZooHypothesis = 2,
          DogFashionDiscoAdultery = 3,
          }
           
          const selectedAlbum = Album.JimmyEatWorldFutures;
          if (selectedAlbum === Album.JimmyEatWorldFutures) {
          console.log("That is a great choice.");
          }
          Try

          The default const enum behavior is to convert any Album.Something to the corresponding number literal, and to remove a reference to the enum from the JavaScript completely.

          ts
          "use strict";
          const selectedAlbum = 1 /* JimmyEatWorldFutures */;
          if (selectedAlbum === 1 /* JimmyEatWorldFutures */) {
          console.log("That is a great choice.");
          }
           
          Try

          With preserveConstEnums set to true, the enum exists at runtime and the numbers are still emitted.

          ts
          "use strict";
          var Album;
          (function (Album) {
          Album[Album["JimmyEatWorldFutures"] = 1] = "JimmyEatWorldFutures";
          Album[Album["TubRingZooHypothesis"] = 2] = "TubRingZooHypothesis";
          Album[Album["DogFashionDiscoAdultery"] = 3] = "DogFashionDiscoAdultery";
          })(Album || (Album = {}));
          const selectedAlbum = 1 /* JimmyEatWorldFutures */;
          if (selectedAlbum === 1 /* JimmyEatWorldFutures */) {
          console.log("That is a great choice.");
          }
           
          Try

          This essentially makes such const enums a source-code feature only, with no runtime traces.

          • Default:

            false

          # preserveValueImports - preserveValueImports

          There are some cases where TypeScript can’t detect that you’re using an import. For example, take the following code:

          ts
          import { Animal } from "./animal.js";
          eval("console.log(new Animal().isDangerous())");

          or code using ‘Compiles to HTML’ languages like Svelte or Vue.

          When combined with isolatedModules: imported types must be marked as type-only because compilers that process single files at a time have no way of knowing whether imports are values that appear unused, or a type that must be removed in order to avoid a runtime crash.

          For example, in the following code TitleComponent is a function and TitleComponentProps is a type with isolatedModules and preserveValueImports are enabled:

          ts
          import { TitleComponent, TitleComponentProps } from "./TitleComponent.js";
          Try

          Which can be fixed by prefixing TitleComponentProps with type to mark it as a type-only import:

          ts
          import { TitleComponent, type TitleComponentProps } from "./TitleComponent.js";
          Try

          # Remove Comments - removeComments

          Strips all comments from TypeScript files when converting into JavaScript. Defaults to false.

          For example, this is a TypeScript file which has a JSDoc comment:

          ts
          /** The translation of 'Hello world' into Portuguese */
          export const helloWorldPTBR = "Olá Mundo";

          When removeComments is set to true:

          ts
          export const helloWorldPTBR = "Olá Mundo";
           
          Try

          Without setting removeComments or having it as false:

          ts
          /** The translation of 'Hello world' into Portuguese */
          export const helloWorldPTBR = "Olá Mundo";
           
          Try

          This means that your comments will show up in the JavaScript code.

          • Default:

            false

          # Source Map - sourceMap

          Enables the generation of sourcemap files. These files allow debuggers and other tools to display the original TypeScript source code when actually working with the emitted JavaScript files. Source map files are emitted as .js.map (or .jsx.map) files next to the corresponding .js output file.

          The .js files will in turn contain a sourcemap comment to indicate where the files are to external tools, for example:

          ts
          // helloWorld.ts
          export declare const helloWorld = "hi";

          Compiling with sourceMap set to true creates the following JavaScript file:

          js
          // helloWorld.js
          "use strict";
          Object.defineProperty(exports, "__esModule", { value: true });
          exports.helloWorld = "hi";
          //# sourceMappingURL=// helloWorld.js.map

          And this also generates this json map:

          json
          // helloWorld.js.map
          {
          "version": 3,
          "file": "ex.js",
          "sourceRoot": "",
          "sources": ["../ex.ts"],
          "names": [],
          "mappings": ";;AAAa,QAAA,UAAU,GAAG,IAAI,CAAA"
          }
          • Default:

            false

          # Source Root - sourceRoot

          Specify the location where a debugger should locate TypeScript files instead of relative source locations. This string is treated verbatim inside the source-map where you can use a path or a URL:

          {
          "": true,
          "": "https://my-website.com/debug/source/"
          }
          }

          Would declare that index.js will have a source file at https://my-website.com/debug/source/index.ts.

            # Strip Internal - stripInternal

            Do not emit declarations for code that has an @internal annotation in its JSDoc comment. This is an internal compiler option; use at your own risk, because the compiler does not check that the result is valid. If you are searching for a tool to handle additional levels of visibility within your d.ts files, look at api-extractor.

            ts
            /**
            * Days available in a week
            * @internal
            */
            export const daysInAWeek = 7;
             
            /** Calculate how much someone earns in a week */
            export function weeklySalary(dayRate: number) {
            return daysInAWeek * dayRate;
            }
            Try

            With the flag set to false (default):

            ts
            /**
            * Days available in a week
            * @internal
            */
            export declare const daysInAWeek = 7;
            /** Calculate how much someone earns in a week */
            export declare function weeklySalary(dayRate: number): number;
             
            Try

            With stripInternal set to true the d.ts emitted will be redacted.

            ts
            /** Calculate how much someone earns in a week */
            export declare function weeklySalary(dayRate: number): number;
             
            Try

            The JavaScript output is still the same.

            • Internal
            • Default:

              false

            #JavaScript Support

            # Allow JS - allowJs

            Allow JavaScript files to be imported inside your project, instead of just .ts and .tsx files. For example, this JS file:

            js
            // @filename: card.js
            export const defaultCardDeck = "Heart";
            Try

            When imported into a TypeScript file will raise an error:

            ts
            // @filename: index.ts
            import { defaultCardDeck } from "./card";
             
            console.log(defaultCardDeck);
            Try

            Imports fine with allowJs enabled:

            ts
            // @filename: index.ts
            import { defaultCardDeck } from "./card";
             
            console.log(defaultCardDeck);
            Try

            This flag can be used as a way to incrementally add TypeScript files into JS projects by allowing the .ts and .tsx files to live along-side existing JavaScript files.

            # Check JS - checkJs

            Works in tandem with allowJs. When checkJs is enabled then errors are reported in JavaScript files. This is the equivalent of including // @ts-check at the top of all JavaScript files which are included in your project.

            For example, this is incorrect JavaScript according to the parseFloat type definition which comes with TypeScript:

            js
            // parseFloat only takes a string
            module.exports.pi = parseFloat(3.124);

            When imported into a TypeScript module:

            ts
            // @filename: constants.js
            module.exports.pi = parseFloat(3.124);
             
            // @filename: index.ts
            import { pi } from "./constants";
            console.log(pi);
            Try

            You will not get any errors. However, if you turn on checkJs then you will get error messages from the JavaScript file.

            ts
            // @filename: constants.js
            Argument of type 'number' is not assignable to parameter of type 'string'.2345Argument of type 'number' is not assignable to parameter of type 'string'.
            module.exports.pi = parseFloat(3.124);
             
            // @filename: index.ts
            import { pi } from "./constants";
            console.log(pi);
            Try

            # Max Node Module JS Depth - maxNodeModuleJsDepth

            The maximum dependency depth to search under node_modules and load JavaScript files.

            This flag is can only be used when allowJs is enabled, and is used if you want to have TypeScript infer types for all of the JavaScript inside your node_modules.

            Ideally this should stay at 0 (the default), and d.ts files should be used to explicitly define the shape of modules. However, there are cases where you may want to turn this on at the expense of speed and potential accuracy.

            • Default:

              0

            #Editor Support

            # Disable Size Limit - disableSizeLimit

            To avoid a possible memory bloat issues when working with very large JavaScript projects, there is an upper limit to the amount of memory TypeScript will allocate. Turning this flag on will remove the limit.

            • Default:

              false

            # Plugins - plugins

            List of language service plugins to run inside the editor.

            Language service plugins are a way to provide additional information to a user based on existing TypeScript files. They can enhance existing messages between TypeScript and an editor, or to provide their own error messages.

            For example:

            VS Code has the ability for a extension to automatically include language service plugins, and so you may have some running in your editor without needing to define them in your tsconfig.json.

              #Interop Constraints

              # Allow Synthetic Default Imports - allowSyntheticDefaultImports

              When set to true, allowSyntheticDefaultImports allows you to write an import like:

              ts
              import React from "react";

              instead of:

              ts
              import * as React from "react";

              When the module does not explicitly specify a default export.

              For example, without allowSyntheticDefaultImports as true:

              ts
              // @filename: utilFunctions.js
              Module '"/home/runner/work/TypeScript-Website/TypeScript-Website/utilFunctions"' has no default export.1192Module '"/home/runner/work/TypeScript-Website/TypeScript-Website/utilFunctions"' has no default export.
              const getStringLength = (str) => str.length;
               
              module.exports = {
              getStringLength,
              };
               
              // @filename: index.ts
              import utils from "./utilFunctions";
               
              const count = utils.getStringLength("Check JS");
              Try

              This code raises an error because there isn’t a default object which you can import. Even though it feels like it should. For convenience, transpilers like Babel will automatically create a default if one isn’t created. Making the module look a bit more like:

              js
              // @filename: utilFunctions.js
              const getStringLength = (str) => str.length;
              const allFunctions = {
              getStringLength,
              };
              module.exports = allFunctions;
              module.exports.default = allFunctions;

              This flag does not affect the JavaScript emitted by TypeScript, it only for the type checking. This option brings the behavior of TypeScript in-line with Babel, where extra code is emitted to make using a default export of a module more ergonomic.

              # ES Module Interop - esModuleInterop

              By default (with esModuleInterop false or not set) TypeScript treats CommonJS/AMD/UMD modules similar to ES6 modules. In doing this, there are two parts in particular which turned out to be flawed assumptions:

              • a namespace import like import * as moment from "moment" acts the same as const moment = require("moment")

              • a default import like import moment from "moment" acts the same as const moment = require("moment").default

              This mis-match causes these two issues:

              • the ES6 modules spec states that a namespace import (import * as x) can only be an object, by having TypeScript treating it the same as = require("x") then TypeScript allowed for the import to be treated as a function and be callable. That’s not valid according to the spec.

              • while accurate to the ES6 modules spec, most libraries with CommonJS/AMD/UMD modules didn’t conform as strictly as TypeScript’s implementation.

              Turning on esModuleInterop will fix both of these problems in the code transpiled by TypeScript. The first changes the behavior in the compiler, the second is fixed by two new helper functions which provide a shim to ensure compatibility in the emitted JavaScript:

              ts
              import * as fs from "fs";
              import _ from "lodash";
              fs.readFileSync("file.txt", "utf8");
              _.chunk(["a", "b", "c", "d"], 2);

              With esModuleInterop disabled:

              ts
              "use strict";
              Object.defineProperty(exports, "__esModule", { value: true });
              const fs = require("fs");
              const lodash_1 = require("lodash");
              fs.readFileSync("file.txt", "utf8");
              lodash_1.default.chunk(["a", "b", "c", "d"], 2);
               
              Try

              With esModuleInterop set to true:

              ts
              "use strict";
              var __createBinding = (this && this.__createBinding) || (Object.create ? (function(o, m, k, k2) {
              if (k2 === undefined) k2 = k;
              Object.defineProperty(o, k2, { enumerable: true, get: function() { return m[k]; } });
              }) : (function(o, m, k, k2) {
              if (k2 === undefined) k2 = k;
              o[k2] = m[k];
              }));
              var __setModuleDefault = (this && this.__setModuleDefault) || (Object.create ? (function(o, v) {
              Object.defineProperty(o, "default", { enumerable: true, value: v });
              }) : function(o, v) {
              o["default"] = v;
              });
              var __importStar = (this && this.__importStar) || function (mod) {
              if (mod && mod.__esModule) return mod;
              var result = {};
              if (mod != null) for (var k in mod) if (k !== "default" && Object.prototype.hasOwnProperty.call(mod, k)) __createBinding(result, mod, k);
              __setModuleDefault(result, mod);
              return result;
              };
              var __importDefault = (this && this.__importDefault) || function (mod) {
              return (mod && mod.__esModule) ? mod : { "default": mod };
              };
              Object.defineProperty(exports, "__esModule", { value: true });
              const fs = __importStar(require("fs"));
              const lodash_1 = __importDefault(require("lodash"));
              fs.readFileSync("file.txt", "utf8");
              lodash_1.default.chunk(["a", "b", "c", "d"], 2);
               
              Try

              Note: The namespace import import * as fs from "fs" only accounts for properties which are owned (basically properties set on the object and not via the prototype chain) on the imported object. If the module you’re importing defines its API using inherited properties, you need to use the default import form (import fs from "fs"), or disable esModuleInterop.

              Note: You can make JS emit terser by enabling importHelpers:

              ts
              "use strict";
              Object.defineProperty(exports, "__esModule", { value: true });
              const tslib_1 = require("tslib");
              const fs = (0, tslib_1.__importStar)(require("fs"));
              const lodash_1 = (0, tslib_1.__importDefault)(require("lodash"));
              fs.readFileSync("file.txt", "utf8");
              lodash_1.default.chunk(["a", "b", "c", "d"], 2);
               
              Try

              Enabling esModuleInterop will also enable allowSyntheticDefaultImports.

              # Force Consistent Casing In File Names - forceConsistentCasingInFileNames

              TypeScript follows the case sensitivity rules of the file system it’s running on. This can be problematic if some developers are working in a case-sensitive file system and others aren’t. If a file attempts to import fileManager.ts by specifying ./FileManager.ts the file will be found in a case-insensitive file system, but not on a case-sensitive file system.

              When this option is set, TypeScript will issue an error if a program tries to include a file by a casing different from the casing on disk.

              • Recommended
              • Default:

                false

              # Isolated Modules - isolatedModules

              While you can use TypeScript to produce JavaScript code from TypeScript code, it’s also common to use other transpilers such as Babel to do this. However, other transpilers only operate on a single file at a time, which means they can’t apply code transforms that depend on understanding the full type system. This restriction also applies to TypeScript’s ts.transpileModule API which is used by some build tools.

              These limitations can cause runtime problems with some TypeScript features like const enums and namespaces. Setting the isolatedModules flag tells TypeScript to warn you if you write certain code that can’t be correctly interpreted by a single-file transpilation process.

              It does not change the behavior of your code, or otherwise change the behavior of TypeScript’s checking and emitting process.

              Some examples of code which does not work when isolatedModules is enabled.

              Exports of Non-Value Identifiers

              In TypeScript, you can import a type and then subsequently export it:

              ts
              import { someType, someFunction } from "someModule";
               
              someFunction();
               
              export { someType, someFunction };
              Try

              Because there’s no value for someType, the emitted export will not try to export it (this would be a runtime error in JavaScript):

              js
              export { someFunction };

              Single-file transpilers don’t know whether someType produces a value or not, so it’s an error to export a name that only refers to a type.

              Non-Module Files

              If isolatedModules is set, all implementation files must be modules (which means it has some form of import/export). An error occurs if any file isn’t a module:

              ts
              function fn() {}
              'index.ts' cannot be compiled under '--isolatedModules' because it is considered a global script file. Add an import, export, or an empty 'export {}' statement to make it a module.1208'index.ts' cannot be compiled under '--isolatedModules' because it is considered a global script file. Add an import, export, or an empty 'export {}' statement to make it a module.
              Try

              This restriction doesn’t apply to .d.ts files.

              References to const enum members

              In TypeScript, when you reference a const enum member, the reference is replaced by its actual value in the emitted JavaScript. Changing this TypeScript:

              ts
              declare const enum Numbers {
              Zero = 0,
              One = 1,
              }
              console.log(Numbers.Zero + Numbers.One);
              Try

              To this JavaScript:

              ts
              "use strict";
              console.log(0 + 1);
               
              Try

              Without knowledge of the values of these members, other transpilers can’t replace the references to Numbers, which would be a runtime error if left alone (since there are no Numbers object at runtime). Because of this, when isolatedModules is set, it is an error to reference an ambient const enum member.

              • Default:

                false

              This is to reflect the same flag in Node.js; which does not resolve the real path of symlinks.

              This flag also exhibits the opposite behavior to Webpack’s resolve.symlinks option (i.e. setting TypeScript’s preserveSymlinks to true parallels setting Webpack’s resolve.symlinks to false, and vice-versa).

              With this enabled, references to modules and packages (e.g. imports and /// <reference type="..." /> directives) are all resolved relative to the location of the symbolic link file, rather than relative to the path that the symbolic link resolves to.

              • Default:

                false

              #Backwards Compatibility

              # Charset - charset

              In prior versions of TypeScript, this controlled what encoding was used when reading text files from disk. Today, TypeScript assumes UTF-8 encoding, but will correctly detect UTF-16 (BE and LE) or UTF-8 BOMs.

              • Deprecated
              • Default:

                utf8

              # Keyof Strings Only - keyofStringsOnly

              This flag changes the keyof type operator to return string instead of string | number when applied to a type with a string index signature.

              This flag is used to help people keep this behavior from before TypeScript 2.9’s release.

              • Deprecated
              • Default:

                false

              • Released:

                2.9

              # No Implicit Use Strict - noImplicitUseStrict

              You shouldn’t need this. By default, when emitting a module file to a non-ES6 target, TypeScript emits a "use strict"; prologue at the top of the file. This setting disables the prologue.

              ts
              define(["require", "exports"], function (require, exports) {
              exports.__esModule = true;
              exports.fn = void 0;
              function fn() { }
              exports.fn = fn;
              });
               
              Try
              ts
              define(["require", "exports"], function (require, exports) {
              "use strict";
              exports.__esModule = true;
              exports.fn = void 0;
              function fn() { }
              exports.fn = fn;
              });
               
              Try
              • Default:

                false

              # No Strict Generic Checks - noStrictGenericChecks

              TypeScript will unify type parameters when comparing two generic functions.

              ts
              type A = <T, U>(x: T, y: U) => [T, U];
              type B = <S>(x: S, y: S) => [S, S];
               
              function f(a: A, b: B) {
              b = a; // Ok
              a = b; // Error
              Type 'B' is not assignable to type 'A'. Types of parameters 'y' and 'y' are incompatible. Type 'U' is not assignable to type 'T'. 'T' could be instantiated with an arbitrary type which could be unrelated to 'U'.2322Type 'B' is not assignable to type 'A'. Types of parameters 'y' and 'y' are incompatible. Type 'U' is not assignable to type 'T'. 'T' could be instantiated with an arbitrary type which could be unrelated to 'U'.
              }
              Try

              This flag can be used to remove that check.

              • Default:

                false

              • Released:

                2.4

              # Out - out

              Use outFile instead.

              The out option computes the final file location in a way that is not predictable or consistent. This option is retained for backward compatibility only and is deprecated.

              # Suppress Excess Property Errors - suppressExcessPropertyErrors

              This disables reporting of excess property errors, such as the one shown in the following example:

              ts
              type Point = { x: number; y: number };
              const p: Point = { x: 1, y: 3, m: 10 };
              Type '{ x: number; y: number; m: number; }' is not assignable to type 'Point'. Object literal may only specify known properties, and 'm' does not exist in type 'Point'.2322Type '{ x: number; y: number; m: number; }' is not assignable to type 'Point'. Object literal may only specify known properties, and 'm' does not exist in type 'Point'.
              Try

              This flag was added to help people migrate to the stricter checking of new object literals in TypeScript 1.6.

              We don’t recommend using this flag in a modern codebase, you can suppress one-off cases where you need it using // @ts-ignore.

              • Default:

                false

              # Suppress Implicit Any Index Errors - suppressImplicitAnyIndexErrors

              Turning suppressImplicitAnyIndexErrors on suppresses reporting the error about implicit anys when indexing into objects, as shown in the following example:

              ts
              const obj = { x: 10 };
              console.log(obj["foo"]);
              Element implicitly has an 'any' type because expression of type '"foo"' can't be used to index type '{ x: number; }'. Property 'foo' does not exist on type '{ x: number; }'.7053Element implicitly has an 'any' type because expression of type '"foo"' can't be used to index type '{ x: number; }'. Property 'foo' does not exist on type '{ x: number; }'.
              Try

              Using suppressImplicitAnyIndexErrors is quite a drastic approach. It is recommended to use a @ts-ignore comment instead:

              ts
              const obj = { x: 10 };
              // @ts-ignore
              console.log(obj["foo"]);
              Try

              #Language and Environment

              # Emit Decorator Metadata - emitDecoratorMetadata

              Enables experimental support for emitting type metadata for decorators which works with the module reflect-metadata.

              For example, here is the JavaScript

              ts
              function LogMethod(
              target: any,
              propertyKey: string | symbol,
              descriptor: PropertyDescriptor
              ) {
              console.log(target);
              console.log(propertyKey);
              console.log(descriptor);
              }
               
              class Demo {
              @LogMethod
              public foo(bar: number) {
              // do nothing
              }
              }
               
              const demo = new Demo();
              Try

              With emitDecoratorMetadata not set to true (default):

              ts
              "use strict";
              var __decorate = (this && this.__decorate) || function (decorators, target, key, desc) {
              var c = arguments.length, r = c < 3 ? target : desc === null ? desc = Object.getOwnPropertyDescriptor(target, key) : desc, d;
              if (typeof Reflect === "object" && typeof Reflect.decorate === "function") r = Reflect.decorate(decorators, target, key, desc);
              else for (var i = decorators.length - 1; i >= 0; i--) if (d = decorators[i]) r = (c < 3 ? d(r) : c > 3 ? d(target, key, r) : d(target, key)) || r;
              return c > 3 && r && Object.defineProperty(target, key, r), r;
              };
              function LogMethod(target, propertyKey, descriptor) {
              console.log(target);
              console.log(propertyKey);
              console.log(descriptor);
              }
              class Demo {
              foo(bar) {
              // do nothing
              }
              }
              __decorate([
              LogMethod
              ], Demo.prototype, "foo", null);
              const demo = new Demo();
               
              Try

              With emitDecoratorMetadata set to true:

              ts
              "use strict";
              var __decorate = (this && this.__decorate) || function (decorators, target, key, desc) {
              var c = arguments.length, r = c < 3 ? target : desc === null ? desc = Object.getOwnPropertyDescriptor(target, key) : desc, d;
              if (typeof Reflect === "object" && typeof Reflect.decorate === "function") r = Reflect.decorate(decorators, target, key, desc);
              else for (var i = decorators.length - 1; i >= 0; i--) if (d = decorators[i]) r = (c < 3 ? d(r) : c > 3 ? d(target, key, r) : d(target, key)) || r;
              return c > 3 && r && Object.defineProperty(target, key, r), r;
              };
              var __metadata = (this && this.__metadata) || function (k, v) {
              if (typeof Reflect === "object" && typeof Reflect.metadata === "function") return Reflect.metadata(k, v);
              };
              function LogMethod(target, propertyKey, descriptor) {
              console.log(target);
              console.log(propertyKey);
              console.log(descriptor);
              }
              class Demo {
              foo(bar) {
              // do nothing
              }
              }
              __decorate([
              LogMethod,
              __metadata("design:type", Function),
              __metadata("design:paramtypes", [Number]),
              __metadata("design:returntype", void 0)
              ], Demo.prototype, "foo", null);
              const demo = new Demo();
               
              Try

              # Experimental Decorators - experimentalDecorators

              Enables experimental support for decorators, which is in stage 2 of the TC39 standardization process.

              Decorators are a language feature which hasn’t yet been fully ratified into the JavaScript specification. This means that the implementation version in TypeScript may differ from the implementation in JavaScript when it it decided by TC39.

              You can find out more about decorator support in TypeScript in the handbook.

              # JSX - jsx

              Controls how JSX constructs are emitted in JavaScript files. This only affects output of JS files that started in .tsx files.

              • react: Emit .js files with JSX changed to the equivalent React.createElement calls
              • react-jsx: Emit .js files with the JSX changed to _jsx calls
              • react-jsxdev: Emit .js files with the JSX to _jsx calls
              • preserve: Emit .jsx files with the JSX unchanged
              • react-native: Emit .js files with the JSX unchanged

              For example

              This sample code:

              tsx
              export const helloWorld = () => <h1>Hello world</h1>;

              Default: "react"

              tsx
              import React from 'react';
              export const helloWorld = () => React.createElement("h1", null, "Hello world");
               
              Try

              Preserve: "preserve"

              tsx
              import React from 'react';
              export const helloWorld = () => <h1>Hello world</h1>;
               
              Try

              React Native: "react-native"

              tsx
              import React from 'react';
              export const helloWorld = () => <h1>Hello world</h1>;
               
              Try

              React 17 transform: "react-jsx"[1]

              tsx
              import { jsx as _jsx } from "react/jsx-runtime";
              import React from 'react';
              export const helloWorld = () => _jsx("h1", { children: "Hello world" }, void 0);
               
              Try

              React 17 dev transform: "react-jsxdev"[1]

              tsx
              import { jsxDEV as _jsxDEV } from "react/jsx-dev-runtime";
              const _jsxFileName = "/home/runner/work/TypeScript-Website/TypeScript-Website/index.tsx";
              import React from 'react';
              export const helloWorld = () => _jsxDEV("h1", { children: "Hello world" }, void 0, false, { fileName: _jsxFileName, lineNumber: 9, columnNumber: 32 }, this);
               
              Try

              # JSX Factory - jsxFactory

              Changes the function called in .js files when compiling JSX Elements using the classic JSX runtime. The most common change is to use "h" or "preact.h" instead of the default "React.createElement" if using preact.

              For example, this TSX file:

              tsx
              import { h } from "preact";
              const HelloWorld = () => <div>Hello</div>;

              With jsxFactory: "h" looks like:

              tsx
              const preact_1 = require("preact");
              const HelloWorld = () => (0, preact_1.h)("div", null, "Hello");
               
              Try

              This option can be used on a per-file basis too similar to Babel’s /** @jsx h */ directive.

              tsx
              /** @jsx h */
              import { h } from "preact";
               
              const HelloWorld = () => <div>Hello</div>;
              Try

              The factory chosen will also affect where the JSX namespace is looked up (for type checking information) before falling back to the global one.

              If the factory is defined as React.createElement (the default), the compiler will check for React.JSX before checking for a global JSX. If the factory is defined as h, it will check for h.JSX before a global JSX.

              # jsxFragmentFactory - jsxFragmentFactory

              Specify the JSX fragment factory function to use when targeting react JSX emit with jsxFactory compiler option is specified, e.g. Fragment.

              For example with this TSConfig:

              {
              "": "esnext",
              "": "commonjs",
              "": "react",
              "": "h",
              "": "Fragment"
              }
              }

              This TSX file:

              tsx
              import { h, Fragment } from "preact";
              const HelloWorld = () => (
              <>
              <div>Hello</div>
              </>
              );

              Would look like:

              tsx
              const preact_1 = require("preact");
              const HelloWorld = () => ((0, preact_1.h)(preact_1.Fragment, null,
              (0, preact_1.h)("div", null, "Hello")));
               
              Try

              This option can be used on a per-file basis too similar to Babel’s /* @jsxFrag h */ directive.

              For example:

              tsx
              /** @jsx h */
              /** @jsxFrag Fragment */
               
              import { h, Fragment } from "preact";
               
              const HelloWorld = () => (
              <>
              <div>Hello</div>
              </>
              );
              Try

              # jsxImportSource - jsxImportSource

              Declares the module specifier to be used for importing the jsx and jsxs factory functions when using jsx as "react-jsx" or "react-jsxdev" which were introduced in TypeScript 4.1.

              With React 17 the library supports a new form of JSX transformation via a separate import.

              For example with this code:

              tsx
              import React from "react";
              function App() {
              return <h1>Hello World</h1>;
              }

              Using this TSConfig:

              {
              "": "esnext",
              "": "commonjs",
              "": "react-jsx"
              }
              }

              The emitted JavaScript from TypeScript is:

              tsx
              "use strict";
              var __importDefault = (this && this.__importDefault) || function (mod) {
              return (mod && mod.__esModule) ? mod : { "default": mod };
              };
              Object.defineProperty(exports, "__esModule", { value: true });
              const jsx_runtime_1 = require("react/jsx-runtime");
              const react_1 = __importDefault(require("react"));
              function App() {
              return (0, jsx_runtime_1.jsx)("h1", { children: "Hello World" }, void 0);
              }
               
              Try

              For example if you wanted to use "jsxImportSource": "preact", you need a tsconfig like:

              {
              "": "esnext",
              "": "commonjs",
              "": "react-jsx",
              "": "preact",
              "": ["preact"]
              }
              }

              Which generates code like:

              tsx
              function App() {
              return (0, jsx_runtime_1.jsx)("h1", { children: "Hello World" }, void 0);
              }
              exports.App = App;
               
              Try

              Alternatively, you can use a per-file pragma to set this option, for example:

              tsx
              /** @jsxImportSource preact */
              export function App() {
              return <h1>Hello World</h1>;
              }

              Would add preact/jsx-runtime as an import for the _jsx factory.

              Note: In order for this to work like you would expect, your tsx file must include an export or import so that it is considered a module.

              # Lib - lib

              TypeScript includes a default set of type definitions for built-in JS APIs (like Math), as well as type definitions for things found in browser environments (like document). TypeScript also includes APIs for newer JS features matching the target you specify; for example the definition for Map is available if target is ES6 or newer.

              You may want to change these for a few reasons:

              • Your program doesn’t run in a browser, so you don’t want the "dom" type definitions
              • Your runtime platform provides certain JavaScript API objects (maybe through polyfills), but doesn’t yet support the full syntax of a given ECMAScript version
              • You have polyfills or native implementations for some, but not all, of a higher level ECMAScript version

              In TypeScript 4.5, lib files can be overriden by npm modules, find out more in the blog.

              High Level libraries

              Name Contents
              ES5 Core definitions for all ES3 and ES5 functionality
              ES2015 Additional APIs available in ES2015 (also known as ES6) - array.find, Promise, Proxy, Symbol, Map, Set, Reflect, etc.
              ES6 Alias for “ES2015”
              ES2016 Additional APIs available in ES2016 - array.include, etc.
              ES7 Alias for “ES2016”
              ES2017 Additional APIs available in ES2017 - Object.entries, Object.values, Atomics, SharedArrayBuffer, date.formatToParts, typed arrays, etc.
              ES2018 Additional APIs available in ES2018 - async iterables, promise.finally, Intl.PluralRules, regexp.groups, etc.
              ES2019 Additional APIs available in ES2019 - array.flat, array.flatMap, Object.fromEntries, string.trimStart, string.trimEnd, etc.
              ES2020 Additional APIs available in ES2020 - string.matchAll, etc.
              ES2021 Additional APIs available in ES2021 - promise.any, string.replaceAll etc.
              ESNext Additional APIs available in ESNext - This changes as the JavaScript specification evolves
              DOM DOM definitions - window, document, etc.
              WebWorker APIs available in WebWorker contexts
              ScriptHost APIs for the Windows Script Hosting System

              Individual library components

              Name
              DOM.Iterable
              ES2015.Core
              ES2015.Collection
              ES2015.Generator
              ES2015.Iterable
              ES2015.Promise
              ES2015.Proxy
              ES2015.Reflect
              ES2015.Symbol
              ES2015.Symbol.WellKnown
              ES2016.Array.Include
              ES2017.object
              ES2017.Intl
              ES2017.SharedMemory
              ES2017.String
              ES2017.TypedArrays
              ES2018.Intl
              ES2018.Promise
              ES2018.RegExp
              ES2019.Array
              ES2019.Object
              ES2019.String
              ES2019.Symbol
              ES2020.String
              ES2020.Symbol.wellknown
              ES2021.Promise
              ES2021.String
              ES2021.Weakref
              ESNext.AsyncIterable
              ESNext.Array
              ESNext.Intl
              ESNext.Symbol

              This list may be out of date, you can see the full list in the TypeScript source code.

              # No Lib - noLib

              Disables the automatic inclusion of any library files. If this option is set, lib is ignored.

              TypeScript cannot compile anything without a set of interfaces for key primitives like: Array, Boolean, Function, IArguments, Number, Object, RegExp, and String. It is expected that if you use noLib you will be including your own type definitions for these.

              • Default:

                false

              • Related:

              # React Namespace - reactNamespace

              Use jsxFactory instead. Specify the object invoked for createElement when targeting react for TSX files.

              • Default:

                React

              # Target - target

              Modern browsers support all ES6 features, so ES6 is a good choice. You might choose to set a lower target if your code is deployed to older environments, or a higher target if your code is guaranteed to run in newer environments.

              The target setting changes which JS features are downleveled and which are left intact. For example, an arrow function () => this will be turned into an equivalent function expression if target is ES5 or lower.

              Changing target also changes the default value of lib. You may “mix and match” target and lib settings as desired, but you could just set target for convenience.

              For developer platforms like Node there are baselines for the target, depending on the type of platform and its version. You can find a set of community organized TSConfigs at tsconfig/bases, which has configurations for common platforms and their versions.

              The special ESNext value refers to the highest version your version of TypeScript supports. This setting should be used with caution, since it doesn’t mean the same thing between different TypeScript versions and can make upgrades less predictable.

              • Default:

                ES3

              • Allowed:
                • es3

                • es5

                • es6/es2015

                • es2016

                • es2017

                • es2018

                • es2019

                • es2020

                • es2021

                • esnext

              • Released:

                1.0

              # Use Define For Class Fields - useDefineForClassFields

              This flag is used as part of migrating to the upcoming standard version of class fields. TypeScript introduced class fields many years before it was ratified in TC39. The latest version of the upcoming specification has a different runtime behavior to TypeScript’s implementation but the same syntax.

              This flag switches to the upcoming ECMA runtime behavior.

              You can read more about the transition in the 3.7 release notes.

              • Default:
                • true if target is ES2022 or higher, including ESNext,

                • false otherwise.

              • Released:

                3.7

              #Compiler Diagnostics

              # Diagnostics - diagnostics

              Used to output diagnostic information for debugging. This command is a subset of extendedDiagnostics which are more user-facing results, and easier to interpret.

              If you have been asked by a TypeScript compiler engineer to give the results using this flag in a compile, in which there is no harm in using extendedDiagnostics instead.

              # explainFiles - explainFiles

              Print names of files which TypeScript sees as a part of your project and the reason they are part of the compilation.

              For example, with this project of just a single index.ts file

              sh
              example
              ├── index.ts
              ├── package.json
              └── tsconfig.json

              Using a tsconfig.json which has explainFiles set to true:

              json
              {
              "compilerOptions": {
              "target": "es5",
              "module": "commonjs",
              "explainFiles": true
              }
              }

              Running TypeScript against this folder would have output like this:

              ❯ tsc node_modules/typescript/lib/lib.d.ts Default library for target 'es5' node_modules/typescript/lib/lib.es5.d.ts Library referenced via 'es5' from file 'node_modules/typescript/lib/lib.d.ts' node_modules/typescript/lib/lib.dom.d.ts Library referenced via 'dom' from file 'node_modules/typescript/lib/lib.d.ts' node_modules/typescript/lib/lib.webworker.importscripts.d.ts Library referenced via 'webworker.importscripts' from file 'node_modules/typescript/lib/lib.d.ts' node_modules/typescript/lib/lib.scripthost.d.ts Library referenced via 'scripthost' from file 'node_modules/typescript/lib/lib.d.ts' index.ts Matched by include pattern '**/*' in 'tsconfig.json'

              The output above show:

              • The initial lib.d.ts lookup based on target, and the chain of .d.ts files which are referenced
              • The index.ts file located via the default pattern of include

              This option is intended for debugging how a file has become a part of your compile.

              • Default:

                false

              • Released:

                4.2

              # Extended Diagnostics - extendedDiagnostics

              You can use this flag to discover where TypeScript is spending its time when compiling. This is a tool used for understanding the performance characteristics of your codebase overall.

              You can learn more about how to measure and understand the output in the performance section of the wiki.

              # Generate CPU Profile - generateCpuProfile

              This option gives you the chance to have TypeScript emit a v8 CPU profile during the compiler run. The CPU profile can provide insight into why your builds may be slow.

              This option can only be used from the CLI via: --generateCpuProfile tsc-output.cpuprofile.

              sh
              npm run tsc --generateCpuProfile tsc-output.cpuprofile

              This file can be opened in a chromium based browser like Chrome or Edge Developer in the CPU profiler section. You can learn more about understanding the compilers performance in the TypeScript wiki section on performance.

              • Default:

                profile.cpuprofile

              • Released:

                3.7

              # List Emitted Files - listEmittedFiles

              Print names of generated files part of the compilation to the terminal.

              This flag is useful in two cases:

              • You want to transpile TypeScript as a part of a build chain in the terminal where the filenames are processed in the next command.
              • You are not sure that TypeScript has included a file you expected, as a part of debugging the file inclusion settings.

              For example:

              example ├── index.ts ├── package.json └── tsconfig.json

              With:

              {
              "": true,
              "": true
              }
              }

              Would echo paths like:

              $ npm run tsc path/to/example/index.js path/to/example/index.d.ts

              Normally, TypeScript would return silently on success.

              • Default:

                false

              # List Files - listFiles

              Print names of files part of the compilation. This is useful when you are not sure that TypeScript has included a file you expected.

              For example:

              example ├── index.ts ├── package.json └── tsconfig.json

              With:

              {
              "": true
              }
              }

              Would echo paths like:

              $ npm run tsc path/to/example/node_modules/typescript/lib/lib.d.ts path/to/example/node_modules/typescript/lib/lib.es5.d.ts path/to/example/node_modules/typescript/lib/lib.dom.d.ts path/to/example/node_modules/typescript/lib/lib.webworker.importscripts.d.ts path/to/example/node_modules/typescript/lib/lib.scripthost.d.ts path/to/example/index.ts

              Note if using TypeScript 4.2, prefer explainFiles which offers an explanation of why a file was added too.

              # Trace Resolution - traceResolution

              When you are trying to debug why a module isn’t being included. You can set traceResolutions to true to have TypeScript print information about its resolution process for each processed file.

              You can read more about this in the handbook.

              • Default:

                false

              • Released:

                2.0

              #Projects

              # Composite - composite

              The composite option enforces certain constraints which make it possible for build tools (including TypeScript itself, under --build mode) to quickly determine if a project has been built yet.

              When this setting is on:

              • The rootDir setting, if not explicitly set, defaults to the directory containing the tsconfig.json file.

              • All implementation files must be matched by an include pattern or listed in the files array. If this constraint is violated, tsc will inform you which files weren’t specified.

              • declaration defaults to true

              You can find documentation on TypeScript projects in the handbook.

              # disableReferencedProjectLoad - disableReferencedProjectLoad

              In multi-project TypeScript programs, TypeScript will load all of the available projects into memory in order to provide accurate results for editor responses which require a full knowledge graph like ‘Find All References’.

              If your project is large, you can use the flag disableReferencedProjectLoad to disable the automatic loading of all projects. Instead, projects are loaded dynamically as you open files through your editor.

              • Default:

                false

              • Released:

                4.0

              # Disable Solution Searching - disableSolutionSearching

              When working with composite TypeScript projects, this option provides a way to declare that you do not want a project to be included when using features like find all references or jump to definition in an editor.

              This flag is something you can use to increase responsiveness in large composite projects.

              • Default:

                false

              • Released:

                3.8

              # Disable Source Project Reference Redirect - disableSourceOfProjectReferenceRedirect

              When working with composite TypeScript projects, this option provides a way to go back to the pre-3.7 behavior where d.ts files were used to as the boundaries between modules. In 3.7 the source of truth is now your TypeScript files.

              • Default:

                false

              • Released:

                3.7

              # Incremental - incremental

              Tells TypeScript to save information about the project graph from the last compilation to files stored on disk. This creates a series of .tsbuildinfo files in the same folder as your compilation output. They are not used by your JavaScript at runtime and can be safely deleted. You can read more about the flag in the 3.4 release notes.

              To control which folders you want to the files to be built to, use the config option tsBuildInfoFile.

              # TS Build Info File - tsBuildInfoFile

              This setting lets you specify a file for storing incremental compilation information as a part of composite projects which enables faster building of larger TypeScript codebases. You can read more about composite projects in the handbook.

              This option offers a way to configure the place where TypeScript keeps track of the files it stores on the disk to indicate a project’s build state — by default, they are in the same folder as your emitted JavaScript.

              #Output Formatting

              # No Error Truncation - noErrorTruncation

              Do not truncate error messages.

              With false, the default.

              ts
              var x: {
              propertyWithAnExceedinglyLongName1: string;
              propertyWithAnExceedinglyLongName2: string;
              propertyWithAnExceedinglyLongName3: string;
              propertyWithAnExceedinglyLongName4: string;
              propertyWithAnExceedinglyLongName5: string;
              propertyWithAnExceedinglyLongName6: string;
              propertyWithAnExceedinglyLongName7: string;
              propertyWithAnExceedinglyLongName8: string;
              };
               
              // String representation of type of 'x' should be truncated in error message
              var s: string = x;
              Type '{ propertyWithAnExceedinglyLongName1: string; propertyWithAnExceedinglyLongName2: string; propertyWithAnExceedinglyLongName3: string; propertyWithAnExceedinglyLongName4: string; propertyWithAnExceedinglyLongName5: string; propertyWithAnExceedinglyLongName6: string; propertyWithAnExceedinglyLongName7: string; propert...' is not assignable to type 'string'.
              Variable 'x' is used before being assigned.
              2322
              2454
              Type '{ propertyWithAnExceedinglyLongName1: string; propertyWithAnExceedinglyLongName2: string; propertyWithAnExceedinglyLongName3: string; propertyWithAnExceedinglyLongName4: string; propertyWithAnExceedinglyLongName5: string; propertyWithAnExceedinglyLongName6: string; propertyWithAnExceedinglyLongName7: string; propert...' is not assignable to type 'string'.
              Variable 'x' is used before being assigned.
              Try

              With true

              ts
              var x: {
              propertyWithAnExceedinglyLongName1: string;
              propertyWithAnExceedinglyLongName2: string;
              propertyWithAnExceedinglyLongName3: string;
              propertyWithAnExceedinglyLongName4: string;
              propertyWithAnExceedinglyLongName5: string;
              propertyWithAnExceedinglyLongName6: string;
              propertyWithAnExceedinglyLongName7: string;
              propertyWithAnExceedinglyLongName8: string;
              };
               
              // String representation of type of 'x' should be truncated in error message
              var s: string = x;
              Type '{ propertyWithAnExceedinglyLongName1: string; propertyWithAnExceedinglyLongName2: string; propertyWithAnExceedinglyLongName3: string; propertyWithAnExceedinglyLongName4: string; propertyWithAnExceedinglyLongName5: string; propertyWithAnExceedinglyLongName6: string; propertyWithAnExceedinglyLongName7: string; propertyWithAnExceedinglyLongName8: string; }' is not assignable to type 'string'.
              Variable 'x' is used before being assigned.
              2322
              2454
              Type '{ propertyWithAnExceedinglyLongName1: string; propertyWithAnExceedinglyLongName2: string; propertyWithAnExceedinglyLongName3: string; propertyWithAnExceedinglyLongName4: string; propertyWithAnExceedinglyLongName5: string; propertyWithAnExceedinglyLongName6: string; propertyWithAnExceedinglyLongName7: string; propertyWithAnExceedinglyLongName8: string; }' is not assignable to type 'string'.
              Variable 'x' is used before being assigned.
              Try
              • Default:

                false

              # Preserve Watch Output - preserveWatchOutput

              Whether to keep outdated console output in watch mode instead of clearing the screen every time a change happened.

              • Internal
              • Default:

                false

              # Pretty - pretty

              Stylize errors and messages using color and context, this is on by default — offers you a chance to have less terse, single colored messages from the compiler.

              • Default:

                true

              #Completeness

              # Skip Default Lib Check - skipDefaultLibCheck

              Use skipLibCheck instead. Skip type checking of default library declaration files.

              • Default:

                false

              # Skip Lib Check - skipLibCheck

              Skip type checking of declaration files.

              This can save time during compilation at the expense of type-system accuracy. For example, two libraries could define two copies of the same type in an inconsistent way. Rather than doing a full check of all d.ts files, TypeScript will type check the code you specifically refer to in your app’s source code.

              A common case where you might think to use skipLibCheck is when there are two copies of a library’s types in your node_modules. In these cases, you should consider using a feature like yarn’s resolutions to ensure there is only one copy of that dependency in your tree or investigate how to ensure there is only one copy by understanding the dependency resolution to fix the issue without additional tooling.

              • Recommended
              • Default:

                false

              • Released:

                2.0

              #Command Line

              #Watch Options

              TypeScript 3.8 shipped a new strategy for watching directories, which is crucial for efficiently picking up changes to node_modules.

              On operating systems like Linux, TypeScript installs directory watchers (as opposed to file watchers) on node_modules and many of its subdirectories to detect changes in dependencies. This is because the number of available file watchers is often eclipsed by the of files in node_modules, whereas there are way fewer directories to track.

              Because every project might work better under different strategies, and this new approach might not work well for your workflows, TypeScript 3.8 introduces a new watchOptions field which allows users to tell the compiler/language service which watching strategies should be used to keep track of files and directories.

              # Assume Changes Only Affect Direct Dependencies - assumeChangesOnlyAffectDirectDependencies

              When this option is enabled, TypeScript will avoid rechecking/rebuilding all truly possibly-affected files, and only recheck/rebuild files that have changed as well as files that directly import them.

              This can be considered a ‘fast & loose’ implementation of the watching algorithm, which can drastically reduce incremental rebuild times at the expense of having to run the full build occasionally to get all compiler error messages.

              • Default:

                false

              • Released:

                3.8

              Watch Options

              You can configure the how TypeScript --watch works. This section is mainly for handling case where fs.watch and fs.watchFile have additional constraints like on Linux. You can read more at Configuring Watch.

              # watchFile - watchFile

              The strategy for how individual files are watched.

              • fixedPollingInterval: Check every file for changes several times a second at a fixed interval.
              • priorityPollingInterval: Check every file for changes several times a second, but use heuristics to check certain types of files less frequently than others.
              • dynamicPriorityPolling: Use a dynamic queue where less-frequently modified files will be checked less often.
              • useFsEvents (the default): Attempt to use the operating system/file system’s native events for file changes.
              • useFsEventsOnParentDirectory: Attempt to use the operating system/file system’s native events to listen for changes on a file’s parent directory
              • Allowed:
                • fixedpollinginterval

                • prioritypollinginterval

                • dynamicprioritypolling

                • fixedchunksizepolling

                • usefsevents

                • usefseventsonparentdirectory

              • Released:

                3.8

              # watchDirectory - watchDirectory

              The strategy for how entire directory trees are watched under systems that lack recursive file-watching functionality.

              • fixedPollingInterval: Check every directory for changes several times a second at a fixed interval.
              • dynamicPriorityPolling: Use a dynamic queue where less-frequently modified directories will be checked less often.
              • useFsEvents (the default): Attempt to use the operating system/file system’s native events for directory changes.
              • Allowed:
                • usefsevents

                • fixedpollinginterval

                • dynamicprioritypolling

                • fixedchunksizepolling

              • Released:

                3.8

              # fallbackPolling - fallbackPolling

              When using file system events, this option specifies the polling strategy that gets used when the system runs out of native file watchers and/or doesn’t support native file watchers.

              • fixedPollingInterval: Check every file for changes several times a second at a fixed interval.
              • priorityPollingInterval: Check every file for changes several times a second, but use heuristics to check certain types of files less frequently than others.
              • dynamicPriorityPolling: Use a dynamic queue where less-frequently modified files will be checked less often.
              • synchronousWatchDirectory: Disable deferred watching on directories. Deferred watching is useful when lots of file changes might occur at once (e.g. a change in node_modules from running npm install), but you might want to disable it with this flag for some less-common setups.
              • Allowed:
                • fixedinterval

                • priorityinterval

                • dynamicpriority

                • fixedchunksize

              • Released:

                3.8

              # synchronousWatchDirectory - synchronousWatchDirectory

              Synchronously call callbacks and update the state of directory watchers on platforms that don`t support recursive watching natively. Instead of giving a small timeout to allow for potentially multiple edits to occur on a file.

              {
              "watchOptions": {
              }
              }

                # excludeDirectories - excludeDirectories

                You can use excludeFiles to drastically reduce the number of files which are watched during --watch. This can be a useful way to reduce the number of open file which TypeScript tracks on Linux.

                {
                "watchOptions": {
                "": ["**/node_modules", "_build", "temp/*"]
                }
                }

                  # excludeFiles - excludeFiles

                  You can use excludeFiles to remove a set of specific files from the files which are watched.

                  {
                  "watchOptions": {
                  "": ["temp/file.ts"]
                  }
                  }

                    Type Acquisition

                    Type Acquisition is only important for JavaScript projects. In TypeScript projects you need to include the types in your projects explicitly. However, for JavaScript projects, the TypeScript tooling will download types for your modules in the background and outside of your node_modules folder.

                    # enable - enable

                    Offers a config for disabling type-acquisition in JavaScript projects:

                    ts
                    {
                    "typeAcquisition": {
                    "enable": false
                    }
                    }

                    This could potentially remove all of the editor auto-completion for your project, if you want to get them back, you can use the Type Search to find @types packages or packages with types in them.

                      # Include - include

                      If you have a JavaScript project where TypeScript needs additional guidance to understand global dependencies, or have disabled the built-in inference via disableFilenameBasedTypeAcquisition.

                      You can use include to specify which types should be used from DefinitelyTyped:

                      json
                      {
                      "typeAcquisition": {
                      "include": ["jquery"]
                      }
                      }

                      # Exclude - exclude

                      Offers a config for disabling the type-acquisition for a certain module in JavaScript projects. This can be useful for projects which include other libraries in testing infrastructure which aren’t needed in the main application.

                      json
                      {
                      "typeAcquisition": {
                      "exclude": ["jest", "mocha"]
                      }
                      }

                      # disableFilenameBasedTypeAcquisition - disableFilenameBasedTypeAcquisition

                      TypeScript’s type acquisition can infer what types should be added based on filenames in a project. This means that having a file like jquery.js in your project would automatically download the types for JQuery from DefinitelyTyped.

                      You can disable this via disableFilenameBasedTypeAcquisition.

                      json
                      {
                      "typeAcquisition": {
                      "disableFilenameBasedTypeAcquisition": true
                      }
                      }