Check ECMAScript Identifier Names

Common errors

• ERR_REQUIRE_ESM

  cause Attempting to `require()` the package in a CommonJS module after version 2.0.0.
  fix Change `const { name } = require('estree-util-is-identifier-name')` to `import { name } from 'estree-util-is-identifier-name'` and ensure your project is configured for ES Modules.

• TypeError: The 'code' argument must be an integer

  cause Passing non-numeric values or incorrect types to `start` or `cont` functions, or using `String.prototype.charCodeAt()` which returns UTF-16 code units (char codes) instead of Unicode code points for astral characters in v3.0.0.
  fix Ensure you pass a valid Unicode code point number (an integer) to `start` and `cont`. Use `String.prototype.codePointAt(index)` to get the correct code point for a character, especially for characters outside the Basic Multilingual Plane.

• SyntaxError: Named export 'default' not found (module 'estree-util-is-identifier-name.js')

  cause Attempting to use a default import, but the package only provides named exports.
  fix Change `import name from 'estree-util-is-identifier-name'` to `import { name } from 'estree-util-is-identifier-name'`.

Warnings

• breaking Version 3.0.0 and above require Node.js 16 or later. Older Node.js versions are no longer supported.
  Fix: Upgrade your Node.js environment to version 16 or higher.
• breaking The `cont` and `start` functions in v3.0.0 now expect Unicode code points as input, not char codes. Passing char codes (e.g., from `String.prototype.charCodeAt()`) will lead to incorrect results or unexpected behavior for astral characters.
  Fix: Ensure you are passing actual Unicode code points (e.g., from `String.prototype.codePointAt()`) to `cont` and `start`.
• breaking The package switched to ESM-only in v2.0.0. Attempting to `require()` this package in a CommonJS context will result in an error.
  Fix: Migrate your codebase to use ES Modules (`import`) or ensure your environment supports dynamic `import()` for CommonJS contexts.
• breaking The package now uses `exports` for module resolution, which may break paths for users relying on internal or non-standard module imports. Avoid using private APIs or deeply nested paths.
  Fix: Always use the main entry points (e.g., `import { name } from 'estree-util-is-identifier-name'`) and avoid direct imports from sub-paths or internal files.

Install

• npm install estree-util-is-identifier-name npm
• yarn add estree-util-is-identifier-name yarn
• pnpm add estree-util-is-identifier-name pnpm

Imports

• name
  wrong:

  import name from 'estree-util-is-identifier-name'

  correct:

  import { name } from 'estree-util-is-identifier-name'

  There is no default export. Use named imports for `name`. This package is ESM-only since v2.0.0, so `require()` will fail.
• start
  wrong:

  const start = require('estree-util-is-identifier-name').start

  correct:

  import { start } from 'estree-util-is-identifier-name'

  ESM-only since v2.0.0. `require()` will fail. In v3.0.0, the `code` parameter expects a Unicode code point, not a char code.
• cont
  wrong:

  import * as estreeUtils from 'estree-util-is-identifier-name'; const { cont } = estreeUtils;

  correct:

  import { cont } from 'estree-util-is-identifier-name'

  Direct named imports are preferred. ESM-only since v2.0.0. In v3.0.0, the `code` parameter expects a Unicode code point, not a char code.
• Options
  wrong:

  import { Options } from 'estree-util-is-identifier-name'

  correct:

  import type { Options } from 'estree-util-is-identifier-name'

  This symbol is a TypeScript type. Use `import type` for type-only imports to prevent potential runtime errors or bundling issues.

Quickstart

Demonstrates how to validate full identifier names and individual code points for starting or continuing an identifier, including the optional JSX support.

import { cont, name, start } from 'estree-util-is-identifier-name';

// Check if a string is a valid identifier name
console.log('Is "$something69" a valid name?', name('$something69')); // => true
console.log('Is "69" a valid name?', name('69')); // => false
console.log('Is "var" a valid name (keywords are not handled here)?', name('var')); // => true

// Check if a code point can start an identifier
// 48 is the Unicode code point for '0'
console.log('Can code point 48 (for "0") start an identifier?', start(48)); // => false
// 97 is the Unicode code point for 'a'
console.log('Can code point 97 (for "a") start an identifier?', start(97)); // => true

// Check if a code point can continue an identifier
// 48 is the Unicode code point for '0'
console.log('Can code point 48 (for "0") continue an identifier?', cont(48)); // => true

// Example with JSX option for names that include hyphens
console.log('Is "my-component" a valid name (without JSX)?', name('my-component')); // => false
console.log('Is "my-component" a valid name (with JSX)?', name('my-component', { jsx: true })); // => true