typescript-estree

TypeScript ESTree

A parser that converts TypeScript source code into an ESTree-compatible form

About

This parser is somewhat generic and robust, and could be used to power any use-case which requires taking TypeScript source code and producing an ESTree-compatible AST.

In fact, it is already used within these hyper-popular open-source projects to power their TypeScript support:

• ESLint, the pluggable linting utility for JavaScript and JSX
• Prettier, an opinionated code formatter

Installation

yarn add -D @typescript-eslint/typescript-estree

API

Parsing

parse(code, options)

Parses the given string of code with the options provided and returns an ESTree-compatible AST.

interface ParseOptions {
  /**
   * create a top-level comments array containing all comments
   */
  comment?: boolean;

  /**
   * An array of modules to turn explicit debugging on for.
   * - 'typescript-eslint' is the same as setting the env var `DEBUG=typescript-eslint:*`
   * - 'eslint' is the same as setting the env var `DEBUG=eslint:*`
   * - 'typescript' is the same as setting `extendedDiagnostics: true` in your tsconfig compilerOptions
   *
   * For convenience, also supports a boolean:
   * - true === ['typescript-eslint']
   * - false === []
   */
  debugLevel?: boolean | ('typescript-eslint' | 'eslint' | 'typescript')[];

  /**
   * Cause the parser to error if it encounters an unknown AST node type (useful for testing).
   * This case only usually occurs when TypeScript releases new features.
   */
  errorOnUnknownASTType?: boolean;

  /**
   * Absolute (or relative to `cwd`) path to the file being parsed.
   */
  filePath?: string;

  /**
   * Enable parsing of JSX.
   * For more details, see https://www.typescriptlang.org/docs/handbook/jsx.html
   *
   * NOTE: this setting does not effect known file types (.js, .jsx, .ts, .tsx, .json) because the
   * TypeScript compiler has its own internal handling for known file extensions.
   *
   * For the exact behavior, see https://github.com/typescript-eslint/typescript-eslint/tree/master/packages/parser#parseroptionsecmafeaturesjsx
   */
  jsx?: boolean;

  /**
   * Controls whether the `loc` information to each node.
   * The `loc` property is an object which contains the exact line/column the node starts/ends on.
   * This is similar to the `range` property, except it is line/column relative.
   */
  loc?: boolean;

  /*
   * Allows overriding of function used for logging.
   * When value is `false`, no logging will occur.
   * When value is not provided, `console.log()` will be used.
   */
  loggerFn?: Function | false;

  /**
   * Controls whether the `range` property is included on AST nodes.
   * The `range` property is a [number, number] which indicates the start/end index of the node in the file contents.
   * This is similar to the `loc` property, except this is the absolute index.
   */
  range?: boolean;

  /**
   * Set to true to create a top-level array containing all tokens from the file.
   */
  tokens?: boolean;

  /*
   * The JSX AST changed the node type for string literals
   * inside a JSX Element from `Literal` to `JSXText`.
   * When value is `true`, these nodes will be parsed as type `JSXText`.
   * When value is `false`, these nodes will be parsed as type `Literal`.
   */
  useJSXTextNode?: boolean;
}

const PARSE_DEFAULT_OPTIONS: ParseOptions = {
  comment: false,
  errorOnUnknownASTType: false,
  filePath: 'estree.ts', // or 'estree.tsx', if you pass jsx: true
  jsx: false,
  loc: false,
  loggerFn: undefined,
  range: false,
  tokens: false,
  useJSXTextNode: false,
};

declare function parse(
  code: string,
  options: ParseOptions = PARSE_DEFAULT_OPTIONS,
): TSESTree.Program;

Example usage:

import { parse } from '@typescript-eslint/typescript-estree';

const code = `const hello: string = 'world';`;
const ast = parse(code, {
  loc: true,
  range: true,
});

parseAndGenerateServices(code, options)

Parses the given string of code with the options provided and returns an ESTree-compatible AST. Accepts additional options which can be used to generate type information along with the AST.

interface ParseAndGenerateServicesOptions extends ParseOptions {
  /**
   * Causes the parser to error if the TypeScript compiler returns any unexpected syntax/semantic errors.
   */
  errorOnTypeScriptSyntacticAndSemanticIssues?: boolean;

  /**
   * When `project` is provided, this controls the non-standard file extensions which will be parsed.
   * It accepts an array of file extensions, each preceded by a `.`.
   */
  extraFileExtensions?: string[];

  /**
   * Absolute (or relative to `tsconfigRootDir`) path to the file being parsed.
   * When `project` is provided, this is required, as it is used to fetch the file from the TypeScript compiler's cache.
   */
  filePath?: string;

  /**
   * Allows the user to control whether or not two-way AST node maps are preserved
   * during the AST conversion process.
   *
   * By default: the AST node maps are NOT preserved, unless `project` has been specified,
   * in which case the maps are made available on the returned `parserServices`.
   *
   * NOTE: If `preserveNodeMaps` is explicitly set by the user, it will be respected,
   * regardless of whether or not `project` is in use.
   */
  preserveNodeMaps?: boolean;

  /**
   * Absolute (or relative to `tsconfigRootDir`) paths to the tsconfig(s).
   * If this is provided, type information will be returned.
   */
  project?: string | string[];

  /**
   * The absolute path to the root directory for all provided `project`s.
   */
  tsconfigRootDir?: string;

  /**
   ***************************************************************************************
   * IT IS RECOMMENDED THAT YOU DO NOT USE THIS OPTION, AS IT CAUSES PERFORMANCE ISSUES. *
   ***************************************************************************************
   *
   * When passed with `project`, this allows the parser to create a catch-all, default program.
   * This means that if the parser encounters a file not included in any of the provided `project`s,
   * it will not error, but will instead parse the file and its dependencies in a new program.
   */
  createDefaultProgram?: boolean;
}

const PARSE_AND_GENERATE_SERVICES_DEFAULT_OPTIONS: ParseOptions = {
  ...PARSE_DEFAULT_OPTIONS,
  errorOnTypeScriptSyntacticAndSemanticIssues: false,
  extraFileExtensions: [],
  preserveNodeMaps: false, // or true, if you do not set this, but pass `project`
  project: undefined,
  tsconfigRootDir: process.cwd(),
};

declare function parseAndGenerateServices(
  code: string,
  options: ParseOptions = PARSE_DEFAULT_OPTIONS,
): TSESTree.Program;

Example usage:

import { parseAndGenerateServices } from '@typescript-eslint/typescript-estree';

const code = `const hello: string = 'world';`;
const ast = parseAndGenerateServices(code, {
  filePath: '/some/path/to/file/foo.ts',
  loc: true,
  project: './tsconfig.json',
  range: true,
});

TSESTree, AST_NODE_TYPES and AST_TOKEN_TYPES

Types for the AST produced by the parse functions.

• TSESTree is a namespace which contains object types representing all of the AST Nodes produced by the parser.
• AST_NODE_TYPES is an enum which provides the values for every single AST node's type property.
• AST_TOKEN_TYPES is an enum which provides the values for every single AST token's type property.

Supported TypeScript Version

We will always endeavor to support the latest stable version of TypeScript.

The version of TypeScript currently supported by this parser is ~3.2.1. This is reflected in the devDependency requirement within the package.json file, and it is what the tests will be run against. We have an open peerDependency requirement in order to allow for experimentation on newer/beta versions of TypeScript.

If you use a non-supported version of TypeScript, the parser will log a warning to the console.

Please ensure that you are using a supported version before submitting any issues/bug reports.

Reporting Issues

Please check the current list of open and known issues and ensure the issue has not been reported before. When creating a new issue provide as much information about your environment as possible. This includes:

• TypeScript version
• The typescript-estree version

AST Alignment Tests

A couple of years after work on this parser began, the TypeScript Team at Microsoft began officially supporting TypeScript parsing via Babel.

I work closely with the TypeScript Team and we are gradually aligning the AST of this project with the one produced by Babel's parser. To that end, I have created a full test harness to compare the ASTs of the two projects which runs on every PR, please see the code for more details.

Build/Test Commands

• npm test - run all tests
• npm run unit-tests - run only unit tests
• npm run ast-alignment-tests - run only Babylon AST alignment tests

Debugging

If you encounter a bug with the parser that you want to investigate, you can turn on the debug logging via setting the environment variable: DEBUG=typescript-eslint:*. I.e. in this repo you can run: DEBUG=typescript-eslint:* yarn lint.

License

TypeScript ESTree inherits from the the original TypeScript ESLint Parser license, as the majority of the work began there. It is licensed under a permissive BSD 2-clause license.

Contributing

See the contributing guide here