--- id: parser sidebar_label: parser --- # `@typescript-eslint/parser` > An [ESLint parser](https://eslint.org/docs/user-guide/configuring/plugins#specifying-parser) used to parse TypeScript code into ESLint-compatible nodes, as well as provide backing TypeScript programs. ✨ This is necessary because TypeScript produces a different, incompatible AST format to the one that ESLint requires to work. For example, this is not valid JavaScript code because it contains the `: number` type annotation: ```ts let x: number = 1; ``` ESLint's native Espree parser would raise an error attempting to parse it. Additionally, because TypeScript is developed separately and with different goals from ESLint, ESTree, and Espree, its AST also represents nodes differently in many cases. TS's AST is optimized for its use case of parsing incomplete code and typechecking. ESTree is unoptimized and intended for "general purpose" use-cases of traversing the AST. :::tip You can select `@typescript-eslint/parser` on the [typescript-eslint playground](/play#showAST=es)'s left sidebar under _Options_ > _AST Explorer_ by selecting _ESTree_. ::: ## Configuration The following additional configuration options are available by specifying them in [`parserOptions`](https://eslint.org/docs/user-guide/configuring/language-options#specifying-parser-options) in your ESLint configuration file. ```ts interface ParserOptions { cacheLifetime?: { glob?: number | 'Infinity'; }; ecmaFeatures?: { jsx?: boolean; globalReturn?: boolean; }; ecmaVersion?: number | 'latest'; emitDecoratorMetadata?: boolean; extraFileExtensions?: string[]; jsxFragmentName?: string | null; jsxPragma?: string | null; lib?: string[]; program?: import('typescript').Program; project?: string | string[] | true; projectFolderIgnoreList?: string[]; tsconfigRootDir?: string; warnOnUnsupportedTypeScriptVersion?: boolean; } ``` ### `cacheLifetime` This option allows you to granularly control our internal cache expiry lengths. You can specify the number of seconds as an integer number, or the string 'Infinity' if you never want the cache to expire. By default cache entries will be evicted after 30 seconds, or will persist indefinitely if the parser infers that it is a single run. ### `ecmaFeatures` Optional additional options to describe how to parse the raw syntax. #### `jsx` > Default `false`. Enable parsing JSX when `true`. More details can be found in the [TypeScript handbook's JSX docs](https://www.typescriptlang.org/docs/handbook/jsx.html). **NOTE:** this setting does not affect known file types (`.js`, `.mjs`, `.cjs`, `.jsx`, `.ts`, `.mts`, `.cts`, `.tsx`, `.json`) because the TypeScript compiler has its own internal handling for known file extensions. The exact behavior is as follows: - `.js`, `.mjs`, `.cjs`, `.jsx`, `.tsx` files are always parsed as if this is `true`. - `.ts`, `.mts`, `.cts` files are always parsed as if this is `false`. - For "unknown" extensions (`.md`, `.vue`): - If `parserOptions.project` is _not_ provided: - The setting will be respected. - If `parserOptions.project` is provided (i.e. you are using rules with type information): - **always parsed as if this is `false`** #### `globalReturn` > Default `false`. This options allows you to tell the parser if you want to allow global `return` statements in your codebase. ### `ecmaVersion` > Default `2018`. Accepts any valid ECMAScript version number or `'latest'`: - A version: es3, es5, es6, es7, es8, es9, es10, es11, es12, es13, ..., or - A year: es2015, es2016, es2017, es2018, es2019, es2020, es2021, es2022, ..., or - `'latest'` When it's a version or a year, the value **must** be a number - so do not include the `es` prefix. Specifies the version of ECMAScript syntax you want to use. This is used by the parser to determine how to perform scope analysis, and it affects the default ### `emitDecoratorMetadata` > Default `undefined`. This option allow you to tell parser to act as if `emitDecoratorMetadata: true` is set in `tsconfig.json`, but without [type-aware linting](../linting/Typed_Linting.mdx). In other words, you don't have to specify `parserOptions.project` in this case, making the linting process faster. ### `extraFileExtensions` > Default `undefined`. This option allows you to provide one or more additional file extensions which should be considered in the TypeScript Program compilation. The default extensions are `['.js', '.mjs', '.cjs', '.jsx', '.ts', '.mts', '.cts', '.tsx']`. Add extensions starting with `.`, followed by the file extension. E.g. for a `.vue` file use `"extraFileExtensions": [".vue"]`. ### `jsxFragmentName` > Default `null` The identifier that's used for JSX fragment elements (after transpilation). If `null`, assumes transpilation will always use a member of the configured `jsxPragma`. This should not be a member expression - just the root identifier (i.e. use `"h"` instead of `"h.Fragment"`). If you provide `parserOptions.project`, you do not need to set this, as it will automatically detected from the compiler. ### `jsxPragma` > Default `'React'` The identifier that's used for JSX Elements creation (after transpilation). If you're using a library other than React (like `preact`), then you should change this value. If you are using the [new JSX transform](https://reactjs.org/blog/2020/09/22/introducing-the-new-jsx-transform.html) you can set this to `null`. This should not be a member expression - just the root identifier (i.e. use `"React"` instead of `"React.createElement"`). If you provide `parserOptions.project`, you do not need to set this, as it will automatically detected from the compiler. ### `lib` > Default `['es2018']` For valid options, see the [TypeScript compiler options](https://www.typescriptlang.org/tsconfig#lib). Specifies the TypeScript `lib`s that are available. This is used by the scope analyser to ensure there are global variables declared for the types exposed by TypeScript. If you provide `parserOptions.project`, you do not need to set this, as it will automatically detected from the compiler. ### `program` > Default `undefined`. This option allows you to programmatically provide an instance of a TypeScript Program object that will provide type information to rules. This will override any programs that would have been computed from `parserOptions.project`. All linted files must be part of the provided program(s). [Refer to the TypeScript Wiki for an example on how to write the `resolveModuleNames` function](https://github.com/Microsoft/TypeScript/wiki/Using-the-Compiler-API#customizing-module-resolution). ### `project` > Default `undefined`. This option allows you to provide a path to your project's `tsconfig.json`. **This setting is required if you want to use rules which require type information**. Relative paths are interpreted relative to the current working directory if `tsconfigRootDir` is not set. If you intend on running ESLint from directories other than the project root, you should consider using `tsconfigRootDir`. - Accepted values: ```js // find the tsconfig.json nearest each source file project: true, // path project: './tsconfig.json'; // glob pattern project: './packages/**/tsconfig.json'; // array of paths and/or glob patterns project: ['./packages/**/tsconfig.json', './separate-package/tsconfig.json']; ``` - If `true`, each source file's parse will find the nearest `tsconfig.json` file to that source file. - This is done by checking that source file's directory tree for the nearest `tsconfig.json`. - If you use project references, TypeScript will not automatically use project references to resolve files. This means that you will have to add each referenced tsconfig to the `project` field either separately, or via a glob. - Note that using wide globs `**` in your `parserOptions.project` may cause performance implications. Instead of globs that use `**` to recursively check all folders, prefer paths that use a single `*` at a time. For more info see [#2611](https://github.com/typescript-eslint/typescript-eslint/issues/2611). - TypeScript will ignore files with duplicate filenames in the same folder (for example, `src/file.ts` and `src/file.js`). TypeScript purposely ignore all but one of the files, only keeping the one file with the highest priority extension (the extension priority order (from highest to lowest) is `.ts`, `.tsx`, `.d.ts`, `.js`, `.jsx`). For more info see #955. - Note that if this setting is specified, you must only lint files that are included in the projects as defined by the provided `tsconfig.json` files. If your existing configuration does not include all of the files you would like to lint, you can create a separate `tsconfig.eslint.json` as follows: ```jsonc { // extend your base config so you don't have to redefine your compilerOptions "extends": "./tsconfig.json", "include": [ "src/**/*.ts", "test/**/*.ts", "typings/**/*.ts", // etc // if you have a mixed JS/TS codebase, don't forget to include your JS files "src/**/*.js" ] } ``` ### `projectFolderIgnoreList` > Default `["**/node_modules/**"]`. This option allows you to ignore folders from being included in your provided list of `project`s. This is useful if you have configured glob patterns, but want to make sure you ignore certain folders. It accepts an array of globs to exclude from the `project` globs. For example, by default it will ensure that a glob like `./**/tsconfig.json` will not match any `tsconfig`s within your `node_modules` folder (some npm packages do not exclude their source files from their published packages). ### `tsconfigRootDir` > Default `undefined`. This option allows you to provide the root directory for relative TSConfig paths specified in the `project` option above. Doing so ensures running ESLint from a directory other than the root will still be able to find your TSConfig. ### `warnOnUnsupportedTypeScriptVersion` > Default `true`. This option allows you to toggle the warning that the parser will give you if you use a version of TypeScript which is not explicitly supported ## Utilities ### `createProgram(configFile, projectDirectory)` This serves as a utility method for users of the `parserOptions.programs` feature to create a TypeScript program instance from a config file. ```ts declare function createProgram( configFile: string, projectDirectory?: string, ): import('typescript').Program; ``` Example usage: ```js title=".eslintrc.js" const parser = require('@typescript-eslint/parser'); module.exports = { parserOptions: { programs: [parser.createProgram('tsconfig.json')], }, }; ```