oxlint-plugin-immutable

Immutability and functional-style lint rules ported from eslint-plugin-functional to Oxlint's JS plugin API. Also works with ESLint flat config via the bundled eslintCompatPlugin wrapper.

Note: Rules that require the TypeScript type checker (deep immutability analysis) are not implemented — Oxlint's JS plugin API operates on AST only. The prefer-immutable-types rule uses ReadonlyShallow enforcement mode, and type-declaration-immutability uses structural AST analysis.

Requirements

• Oxlint >= 1.0.0 (requires jsPlugins support)
• Node.js >= 18

Installation

npm add -D oxlint-plugin-immutable
# or
bun add -d oxlint-plugin-immutable

Usage with Oxlint

Add the plugin to jsPlugins and enable the rules you want:

// .oxlintrc.json
{
  "jsPlugins": ["./node_modules/oxlint-plugin-immutable/dist/index.js"],
  "rules": {
    "oxlint-plugin-immutable/no-let": "error",
    "oxlint-plugin-immutable/no-throw-statements": "error",
    "oxlint-plugin-immutable/type-declaration-immutability": "error",
    "oxlint-plugin-immutable/immutable-data": "error"
  }
}

Usage with ESLint

// eslint.config.mjs
import immutablePlugin from "oxlint-plugin-immutable/dist/index.js";

export default [
  {
    plugins: { functional: immutablePlugin },
    rules: immutablePlugin.configs.recommended.rules,
  },
];

Rules

The Recommended column shows the severity used in plugin.configs.recommended. Rules with — are implemented but not included in the recommended config.

| Rule | Description | Recommended | |---|---|---| | no-let | Disallow let declarations — prefer const | error | | no-throw-statements | Disallow throw statements | error | | prefer-property-signatures | Prefer property signatures over method signatures in types | error | | prefer-immutable-types | Enforce ReadonlyShallow on parameters, return types, and variables (AST-only) | error | | type-declaration-immutability | Type aliases and interfaces must be at least ReadonlyShallow | error | | no-promise-reject | Disallow Promise.reject() | — | | immutable-data | Disallow mutating methods on arrays/objects (push, splice, etc.) | — | | readonly-type | Enforce readonly on TypeScript type members | — |

License

MIT