Registry / testing / eslint-plugin-better-mutation

eslint-plugin-better-mutation

library2.1.0jsnpmunverified

ESLint plugin (v2.1.0) that controls where mutation is allowed in JavaScript/TypeScript, preventing unsafe reassignment of shared variables (globals, parameters, closed-over variables) while permitting safe mutation of locally declared variables. Designed for functional programming style, with support for flat config (ESLint >=9) and classic config. Differentiates from eslint-plugin-immutable by allowing local mutation and providing safer defaults. Active development, monthly releases, peer dep eslint >=6.

testing devops

npm install eslint-plugin-better-mutation

github ↗package ↗

INSTALL

IMPORT

SIG · ESLINT-PLUGIN-BETT

eslint-plugin-better-mutation

testingjavascriptv2.1.0

Install

—

Import

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Disk

—

Pass rate

0/ 6

Env Coverage0 / 6

glibc

18–22

musl

18–22

Install & Compatibility

Where this runs

tested against v? · npm install

Install × environment matrix

Each cell = how many times install + import succeeded across repeated harness runs. Partial = flaky.
glibc = Debian/Ubuntu slim · musl = Alpine Linux

musl

node 18–226 runs

build_error

glibc

node 18–226 runs

build_error

Code

Verified usage

Verified import paths — ran on the pinned version, not inferred.

default

✓ import pluginBetterMutation from "eslint-plugin-better-mutation"

✗ const pluginBetterMutation = require("eslint-plugin-better-mutation")

ESM default import. For CommonJS use require('eslint-plugin-better-mutation') in eslint.config.cjs. Flat config requires ESM.

rules

✓ import { rules } from "eslint-plugin-better-mutation"

✗ const rules = require("eslint-plugin-better-mutation").rules

Named export for direct rule access. Not needed if using plugin object.

configs

✓ import { configs } from "eslint-plugin-better-mutation"

Named export for configs; used in flat config. CommonJS: const { configs } = require('eslint-plugin-better-mutation').

Shows minimal ESLint flat config (ESM) with two mutation rules enabled.

import pluginBetterMutation from "eslint-plugin-better-mutation"; export default [ { name: "my-project", plugins: { "better-mutation": pluginBetterMutation, }, rules: { "better-mutation/no-mutating-functions": "error", "better-mutation/no-mutating-methods": "error", }, }, ];

Debug

Known issues

gotchaThe rule 'no-param-reassign' is NOT the same as this plugin; this plugin treats parameter reassignment as unsafe while allowing local variable mutation.

fix

Use eslint-plugin-better-mutation rules instead of core 'no-param-reassign' for FP-focused mutation control.

affects: >=1.0.0

gotchaCommonJS module.exports assignment is allowed by default, but other global assignments are errors. This can be surprising if you expect all reassignment to be blocked.

fix

To block module.exports assignment, configure the rule with exemptedModuleExports: false.

affects: >=1.0.0

gotchaDestructured properties are not considered safe for reassignment; the rule will flag '({ prop }) => { prop = 1; }' even though prop is a local copy.

fix

Avoid reassigning destructured parameters; treat them as read-only.

affects: >=1.0.0

deprecatedThe 'recommended' config from this plugin is deprecated in favor of flat config's 'extends' approach. Use 'plugin:better-mutation/recommended' in classic config only.

fix

Migrate to flat config and reference configs.recommended.

affects: =2.0.0

Errors

Common errors & fixes

ESLint couldn't find the config "plugin:better-mutation/recommended".

Using classic config string plugin name incorrectly or version mismatch.

fix

Ensure eslint-plugin-better-mutation is installed and in .eslintrc use the full string "plugin:better-mutation/recommended".

Cannot find module 'eslint-plugin-better-mutation'

Package not installed or not in node_modules.

fix

Run 'npm install --save-dev eslint-plugin-better-mutation' and verify it appears in package.json.

Error: Cannot read properties of undefined (reading 'no-mutating-functions')

Importing plugin incorrectly; the plugin object is not loaded as expected.

fix

Use the default import: 'import pluginBetterMutation from "eslint-plugin-better-mutation"'.

Upgrade

Version history

2.1.0latest on npm

Audit

Dependencies

eslintrequiredpeer dependency required to run plugin rules

Agent activity

4 hits · last 30 days

node

Resources

githubhttps://github.com/sloops77/eslint-plugin-better-mutation ↗

packagehttps://www.npmjs.com/package/eslint-plugin-better-mutation ↗