# eslint-visitor-keys [![npm version](https://img.shields.io/npm/v/eslint-visitor-keys.svg)](https://www.npmjs.com/package/eslint-visitor-keys) [![Downloads/month](https://img.shields.io/npm/dm/eslint-visitor-keys.svg)](http://www.npmtrends.com/eslint-visitor-keys) [![Build Status](https://github.com/eslint/js/workflows/CI/badge.svg)](https://github.com/eslint/js/actions) Constants and utilities about visitor keys to traverse AST. ## 💿 Installation Use [npm] to install. ```bash $ npm install eslint-visitor-keys ``` ### Requirements - [Node.js] `^18.18.0`, `^20.9.0`, or `>=21.1.0` ## 📖 Usage To use in an ESM file: ```js import * as evk from "eslint-visitor-keys" ``` To use in a CommonJS file: ```js const evk = require("eslint-visitor-keys") ``` ### evk.KEYS > type: `{ [type: string]: string[] | undefined }` Visitor keys. This keys are frozen. This is an object. Keys are the type of [ESTree] nodes. Their values are an array of property names which have child nodes. For example: ``` console.log(evk.KEYS.AssignmentExpression) // → ["left", "right"] ``` ### evk.getKeys(node) > type: `(node: object) => string[]` Get the visitor keys of a given AST node. This is similar to `Object.keys(node)` of ES Standard, but some keys are excluded: `parent`, `leadingComments`, `trailingComments`, and names which start with `_`. This will be used to traverse unknown nodes. For example: ```js const node = { type: "AssignmentExpression", left: { type: "Identifier", name: "foo" }, right: { type: "Literal", value: 0 } } console.log(evk.getKeys(node)) // → ["type", "left", "right"] ``` ### evk.unionWith(additionalKeys) > type: `(additionalKeys: object) => { [type: string]: string[] | undefined }` Make the union set with `evk.KEYS` and the given keys. - The order of keys is, `additionalKeys` is at first, then `evk.KEYS` is concatenated after that. - It removes duplicated keys as keeping the first one. For example: ```js console.log(evk.unionWith({ MethodDefinition: ["decorators"] })) // → { ..., MethodDefinition: ["decorators", "key", "value"], ... } ``` ## 📰 Change log See [GitHub releases](https://github.com/eslint/js/releases). ## 🍻 Contributing Welcome. See [ESLint contribution guidelines](https://eslint.org/docs/developer-guide/contributing/). ### Development commands - `npm test` runs tests and measures code coverage. - `npm run lint` checks source codes with ESLint. - `npm run test:open-coverage` opens the code coverage report of the previous test with your default browser. [npm]: https://www.npmjs.com/ [Node.js]: https://nodejs.org/ [ESTree]: https://github.com/estree/estree ## Sponsors The following companies, organizations, and individuals support ESLint's ongoing maintenance and development. [Become a Sponsor](https://eslint.org/donate) to get your logo on our READMEs and [website](https://eslint.org/sponsors).