eslint-plugin-immutable-2

ESLint plugin for teams that want TypeScript-first immutability and functional-style conventions in modern flat config projects.

The plugin ships focused flat-config presets with parser setup already wired in. Typed parser services remain opt-in so consumers can decide when they want the extra semantic precision.

Table of contents

1. Installation
2. Quick start (flat config)
3. Presets
4. Configuration examples by preset
5. Type-aware precision
6. Rules
7. Contributors ✨

Installation

npm install --save-dev eslint-plugin-immutable-2 typescript

@typescript-eslint/parser is loaded automatically by plugin presets.

Compatibility

• Supported ESLint versions: 9.x and 10.x
• Config system: Flat Config only (eslint.config.*)
• Node.js runtime: >=22.0.0

Quick start (flat config)

import immutable from "eslint-plugin-immutable-2";

export default [immutable.configs.recommended];

That is enough for the default JS/TS preset file globs (**/*.{js,cjs,mjs,jsx,ts,tsx,mts,cts}).

Presets

This plugin intentionally exports five presets:

Preset	Config key	Use when
🟢 Functional Lite	immutable.configs["functional-lite"]	You want a moderate step up from immutable with lightweight structural functional rules.
🟡 Functional	immutable.configs.functional	You want the strict functional tier without turning on every rule in the plugin.
🟠 Immutable	immutable.configs.immutable	You want the broader immutable baseline with no-let, readonly typing, and method-shape discipline.
🔵 Recommended	immutable.configs.recommended	You want the default low-friction entrypoint focused on high-signal mutation hazards.
🟣 All	immutable.configs.all	You want every rule in this plugin enabled.

Configuration examples by preset

import immutable from "eslint-plugin-immutable-2";

export default [
 // Default low-friction starting point.
 immutable.configs.recommended,

 // Broader immutable baseline with readonly typing and declaration discipline.
 // immutable.configs.immutable,

 // Small structural functional step-up on top of the immutable baseline.
 // immutable.configs["functional-lite"],

 // Strict functional-style coverage without enabling every rule.
 // immutable.configs.functional,

 // Every rule in the plugin.
 // immutable.configs.all,
];

Parser setup behavior

Each preset already includes:

• files: ["**/*.{js,cjs,mjs,jsx,ts,tsx,mts,cts}"]
• languageOptions.parser (@typescript-eslint/parser)
• languageOptions.parserOptions:
  • ecmaVersion: "latest"
  • sourceType: "module"

End users usually do not need to wire parser config manually.

If you need custom parser options (for example project, projectService, or tsconfigRootDir), extend a preset:

import immutable from "eslint-plugin-immutable-2";

const recommended = immutable.configs.recommended;

export default [
 {
  ...recommended,
  languageOptions: {
   ...recommended.languageOptions,
   parserOptions: {
    ...recommended.languageOptions?.parserOptions,
    projectService: true,
   },
  },
 },
];

Type-aware precision

The plugin presets already set the parser and base parser options, but they do not automatically enable project/projectService for you.

If you want the most accurate checker-backed behavior from rules such as immutable-data and the implicit-array inference branch of readonly-array, extend a preset with typed parser services:

import immutable from "eslint-plugin-immutable-2";

export default [
 {
  ...recommended,
  languageOptions: {
   ...recommended.languageOptions,
   parserOptions: {
    ...recommended.languageOptions?.parserOptions,
    projectService: true,
   },
  },
 },
];

Without parser services, the plugin still loads and syntax-first rules still run, but checker-backed branches may fall back to conservative behavior.

The plugin does not currently expose any custom settings.immutable runtime switches. Behavior is controlled through preset choice and per-rule options.

Rules

• Fix legend:
  • 🔧 = autofixable
  • 💡 = suggestions available
  • — = report only
• Preset key legend:
  • 🟢 — immutable.configs["functional-lite"]
  • 🟡 — immutable.configs.functional
  • 🟠 — immutable.configs.immutable
  • 🔵 — immutable.configs.recommended
  • 🟣 — immutable.configs.all

Rule	Fix	Preset key
immutable-data	—	🟢 🟡 🟠 🔵 🟣
no-abort-controller-mutation	—	🟢 🟡 🟠 🔵 🟣
no-atomics-mutation	—	🟢 🟡 🟠 🔵 🟣
no-buffer-mutation	—	🟢 🟡 🟠 🔵 🟣
no-cache-api-mutation	—	🟢 🟡 🟠 🔵 🟣
no-class	—	🟡 🟣
no-conditional-statement	—	🟢 🟡 🟣
no-cookie-mutation	—	🟢 🟡 🟠 🔵 🟣
no-data-view-mutation	—	🟢 🟡 🟠 🔵 🟣
no-date-mutation	—	🟢 🟡 🟠 🔵 🟣
no-dom-token-list-mutation	—	🟢 🟡 🟠 🔵 🟣
no-expression-statement	—	🟡 🟣
no-form-data-mutation	—	🟢 🟡 🟠 🔵 🟣
no-headers-mutation	—	🟢 🟡 🟠 🔵 🟣
no-history-mutation	—	🟢 🟡 🟠 🔵 🟣
no-let	💡	🟢 🟡 🟠 🟣
no-location-mutation	—	🟢 🟡 🟠 🔵 🟣
no-loop-statement	—	🟢 🟡 🟣
no-map-set-mutation	—	🟢 🟡 🟠 🔵 🟣
no-method-signature	💡	🟢 🟡 🟠 🟣
no-mixed-interface	—	🟢 🟡 🟣
no-process-env-mutation	—	🟢 🟡 🟠 🔵 🟣
no-reflect-mutation	—	🟢 🟡 🟠 🔵 🟣
no-regexp-lastindex-mutation	—	🟢 🟡 🟠 🔵 🟣
no-reject	—	🟣
no-stateful-regexp	—	🟢 🟡 🟠 🔵 🟣
no-storage-mutation	—	🟢 🟡 🟠 🔵 🟣
no-this	—	🟡 🟣
no-throw	—	🟡 🟣
no-try	—	🟡 🟣
no-typed-array-mutation	—	🟢 🟡 🟠 🔵 🟣
no-url-mutation	—	🟢 🟡 🟠 🔵 🟣
no-url-search-params-mutation	—	🟢 🟡 🟠 🔵 🟣
readonly-array	🔧	🟢 🟡 🟠 🟣
readonly-keyword	🔧	🟢 🟡 🟠 🟣

Contributors ✨

Thanks goes to these wonderful people (emoji key):

Nick2bad4u 🐛 💻 📖 🤔 🚇 🚧 👀 ⚠️ 🔧	Snyk bot 🛡️ 🚇 🚧 👀	StepSecurity Bot 🛡️ 🚇 🚧	dependabot[bot] 🚇 🛡️
github-actions[bot] 💻 🚇