TypeScript ESTree
A parser that converts TypeScript source code into an ESTree-compatible form
## Getting Started
**[You can find our Getting Started docs here](https://typescript-eslint.io/docs/linting)**
## 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](https://eslint.org), the pluggable linting utility for JavaScript and JSX
- [Prettier](https://prettier.io), an opinionated code formatter
## Installation
```sh
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.
```ts
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/main/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;
}
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,
};
declare function parse(
code: string,
options: ParseOptions = PARSE_DEFAULT_OPTIONS,
): TSESTree.Program;
```
Example usage:
```js
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.
```ts
interface ParseAndGenerateServicesOptions extends ParseOptions {
/**
* Causes the parser to error if the TypeScript compiler returns any unexpected syntax/semantic errors.
*/
errorOnTypeScriptSyntacticAndSemanticIssues?: boolean;
/**
* ***EXPERIMENTAL FLAG*** - Use this at your own risk.
*
* Causes TS to use the source files for referenced projects instead of the compiled .d.ts files.
* This feature is not yet optimized, and is likely to cause OOMs for medium to large projects.
*
* This flag REQUIRES at least TS v3.9, otherwise it does nothing.
*
* See: https://github.com/typescript-eslint/typescript-eslint/issues/2094
*/
EXPERIMENTAL_useSourceOfProjectReferenceRedirect?: 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[];
/**
* If you provide a glob (or globs) to the project option, you can use this option to ignore certain folders from
* being matched by the globs.
* This accepts an array of globs to ignore.
*
* By default, this is set to ["/node_modules/"]
*/
projectFolderIgnoreList?: string[];
/**
* The absolute path to the root directory for all provided `project`s.
*/
tsconfigRootDir?: string;
/**
* An array of one or more instances of TypeScript Program objects to be used for type information.
* This overrides any program or programs that would have been computed from the `project` option.
* All linted files must be part of the provided program(s).
*/
programs?: Program[];
/**
***************************************************************************************
* 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;
/**
* ESLint (and therefore typescript-eslint) is used in both "single run"/one-time contexts,
* such as an ESLint CLI invocation, and long-running sessions (such as continuous feedback
* on a file in an IDE).
*
* When typescript-eslint handles TypeScript Program management behind the scenes, this distinction
* is important because there is significant overhead to managing the so called Watch Programs
* needed for the long-running use-case.
*
* When allowAutomaticSingleRunInference is enabled, we will use common heuristics to infer
* whether or not ESLint is being used as part of a single run.
*/
allowAutomaticSingleRunInference?: boolean;
/**
* Path to a file exporting a custom ModuleResolver.
*/
moduleResolver?: string;
}
interface ParserServices {
program: ts.Program;
esTreeNodeToTSNodeMap: WeakMap;
tsNodeToESTreeNodeMap: WeakMap;
hasFullTypeInformation: boolean;
}
interface ParseAndGenerateServicesResult {
ast: TSESTree.Program;
services: ParserServices;
}
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,
projectFolderIgnoreList: ['/node_modules/'],
tsconfigRootDir: process.cwd(),
};
declare function parseAndGenerateServices(
code: string,
options: ParseOptions = PARSE_DEFAULT_OPTIONS,
): ParseAndGenerateServicesResult;
```
Example usage:
```js
import { parseAndGenerateServices } from '@typescript-eslint/typescript-estree';
const code = `const hello: string = 'world';`;
const { ast, services } = parseAndGenerateServices(code, {
filePath: '/some/path/to/file/foo.ts',
loc: true,
project: './tsconfig.json',
range: true,
});
```
#### `parseWithNodeMaps(code, options)`
Parses the given string of code with the options provided and returns both the ESTree-compatible AST as well as the node maps.
This allows you to work with both ASTs without the overhead of types that may come with `parseAndGenerateServices`.
```ts
interface ParseWithNodeMapsResult {
ast: TSESTree.Program;
esTreeNodeToTSNodeMap: ParserServices['esTreeNodeToTSNodeMap'];
tsNodeToESTreeNodeMap: ParserServices['tsNodeToESTreeNodeMap'];
}
declare function parseWithNodeMaps(
code: string,
options: ParseOptions = PARSE_DEFAULT_OPTIONS,
): ParseWithNodeMapsResult;
```
Example usage:
```js
import { parseWithNodeMaps } from '@typescript-eslint/typescript-estree';
const code = `const hello: string = 'world';`;
const { ast, esTreeNodeToTSNodeMap, tsNodeToESTreeNodeMap } = parseWithNodeMaps(
code,
{
loc: true,
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.
### Utilities
#### `createProgram(configFile, projectDirectory)`
This serves as a utility method for users of the `ParseOptions.programs` feature to create a TypeScript program instance from a config file.
```ts
declare function createProgram(
configFile: string,
projectDirectory: string = process.cwd(),
): import('typescript').Program;
```
Example usage:
```js
const tsESTree = require('@typescript-eslint/typescript-estree');
const program = tsESTree.createProgram('tsconfig.json');
const code = `const hello: string = 'world';`;
const { ast, services } = parseAndGenerateServices(code, {
filePath: '/some/path/to/file/foo.ts',
loc: true,
program,
range: true,
});
```
## Supported TypeScript Version
See the [Supported TypeScript Version](../../README.md#supported-typescript-version) section in the project root.
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](https://blogs.msdn.microsoft.com/typescript/2018/08/27/typescript-and-babel-7/).
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](https://github.com/typescript-eslint/typescript-eslint/tree/main/packages/typescript-estree/tests/ast-alignment) for more details.
## 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](../../CONTRIBUTING.md)