106 lines
2.7 KiB
Markdown
106 lines
2.7 KiB
Markdown
# eslint-visitor-keys
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[](https://www.npmjs.com/package/eslint-visitor-keys)
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[](http://www.npmtrends.com/eslint-visitor-keys)
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[](https://github.com/eslint/eslint-visitor-keys/actions)
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Constants and utilities about visitor keys to traverse AST.
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## 💿 Installation
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Use [npm] to install.
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```bash
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$ npm install eslint-visitor-keys
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```
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### Requirements
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- [Node.js] `^12.22.0`, `^14.17.0`, or `>=16.0.0`
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## 📖 Usage
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To use in an ESM file:
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```js
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import * as evk from "eslint-visitor-keys"
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```
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To use in a CommonJS file:
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```js
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const evk = require("eslint-visitor-keys")
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```
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### evk.KEYS
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> type: `{ [type: string]: string[] | undefined }`
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Visitor keys. This keys are frozen.
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This is an object. Keys are the type of [ESTree] nodes. Their values are an array of property names which have child nodes.
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For example:
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```
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console.log(evk.KEYS.AssignmentExpression) // → ["left", "right"]
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```
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### evk.getKeys(node)
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> type: `(node: object) => string[]`
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Get the visitor keys of a given AST node.
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This is similar to `Object.keys(node)` of ES Standard, but some keys are excluded: `parent`, `leadingComments`, `trailingComments`, and names which start with `_`.
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This will be used to traverse unknown nodes.
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For example:
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```js
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const node = {
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type: "AssignmentExpression",
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left: { type: "Identifier", name: "foo" },
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right: { type: "Literal", value: 0 }
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}
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console.log(evk.getKeys(node)) // → ["type", "left", "right"]
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```
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### evk.unionWith(additionalKeys)
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> type: `(additionalKeys: object) => { [type: string]: string[] | undefined }`
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Make the union set with `evk.KEYS` and the given keys.
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- The order of keys is, `additionalKeys` is at first, then `evk.KEYS` is concatenated after that.
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- It removes duplicated keys as keeping the first one.
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For example:
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```js
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console.log(evk.unionWith({
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MethodDefinition: ["decorators"]
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})) // → { ..., MethodDefinition: ["decorators", "key", "value"], ... }
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```
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## 📰 Change log
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See [GitHub releases](https://github.com/eslint/eslint-visitor-keys/releases).
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## 🍻 Contributing
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Welcome. See [ESLint contribution guidelines](https://eslint.org/docs/developer-guide/contributing/).
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### Development commands
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- `npm test` runs tests and measures code coverage.
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- `npm run lint` checks source codes with ESLint.
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- `npm run test:open-coverage` opens the code coverage report of the previous test with your default browser.
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[npm]: https://www.npmjs.com/
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[Node.js]: https://nodejs.org/
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[ESTree]: https://github.com/estree/estree
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