@e18e/eslint-plugin

The official e18e ESLint plugin for modernizing JavaScript/TypeScript code and improving performance.

This plugin focuses on applying the e18e community's best practices and advise to JavaScript/TypeScript codebases.

Overview

There are a few categories of rules in this plugin:

• Modernization - New syntax and APIs which improve code readability and performance
• Module replacements - Community recommended alternatives to popular libraries, focused on performance and size
• Performance improvements - Patterns that can be optimized for better runtime performance

Each of these can be enabled individually, or you can use the recommended configuration to enable all rules.

Installation

npm install --save-dev @e18e/eslint-plugin

Usage

Add the plugin to your eslint.config.js:

import e18e from '@e18e/eslint-plugin';

export default [
  // Use the recommended configuration (includes all categories)
  e18e.configs.recommended,

  // Or use specific category configurations
  e18e.configs.modernization,
  e18e.configs.moduleReplacements,
  e18e.configs.performanceImprovements,

  // Or configure rules manually
  {
    plugins: {
      e18e
    },
    rules: {
      'e18e/prefer-array-at': 'error',
      'e18e/prefer-array-fill': 'error',
      'e18e/prefer-includes': 'error'
    }
  }
];

Usage with oxlint

If you're using oxlint, you can enable the e18e plugin by adding it to your .oxlintrc.json file:

{
  "jsPlugins": ["@e18e/eslint-plugin"],
  "rules": {
    "e18e/prefer-includes": "error"
  }
}

You can enable the recommended configuration by copying the rules from each of the ESLint configuration files into your .oxlintrc.json file.

• modernization configuration
• module replacements configuration
• performance improvements configuration

Copying these rules into your rules object will achieve the same effect as using the recommended configuration in ESLint.

Note

Our type-aware rules depend on TypeScript ESLint's parser, which means they will not work with oxlint at this time.

Linting package.json

Some rules (e.g. ban-dependencies) can be used against your package.json.

You can achieve this by using @eslint/json or jsonc-eslint-parser.

For example, with @eslint/json and eslint.config.js:

import e18e from '@e18e/eslint-plugin';
import json from '@eslint/json';
import {defineConfig} from 'eslint/config';

export default defineConfig([
  {
    files: ['package.json'],
    language: 'json/json',
    plugins: {
      e18e,
      json
    },
    extends: ['e18e/recommended'],
  }
]);

Or with jsonc-eslint-parser and eslint.config.js:

import e18e from '@e18e/eslint-plugin';
import jsonParser from 'jsonc-eslint-parser';
import {defineConfig} from 'eslint/config';

export default defineConfig([
  {
    files: ['package.json'],
    languageOptions: {
      parser: jsonParser
    },
    plugins: {
      e18e
    },
    extends: ['e18e/recommended'],
  }
]);

Read more at the @eslint/json docs and jsonc-eslint-parser docs.

Rules

Legend:

• ✅ = Yes / Enabled
• ✖️ = No / Disabled
• 💡 = Has suggestions (requires user confirmation for fixes)
• 🔶 = Optionally uses types (works without TypeScript but more powerful with it)

Modernization

Rule	Description	Recommended	Fixable	Requires Types
prefer-array-at	Prefer Array.prototype.at() over length-based indexing	✅	✅	🔶
prefer-array-fill	Prefer Array.prototype.fill() over Array.from() or map() with constant values	✅	✅	✖️
prefer-includes	Prefer .includes() over indexOf() comparisons for arrays and strings	✅	✅	✖️
prefer-array-to-reversed	Prefer Array.prototype.toReversed() over copying and reversing arrays	✅	✅	🔶
prefer-array-to-sorted	Prefer Array.prototype.toSorted() over copying and sorting arrays	✅	✅	🔶
prefer-array-to-spliced	Prefer Array.prototype.toSpliced() over copying and splicing arrays	✅	✅	✖️
prefer-exponentiation-operator	Prefer the exponentiation operator ** over Math.pow()	✅	✅	✖️
prefer-nullish-coalescing	Prefer nullish coalescing operator (?? and ??=) over verbose null checks	✅	✅	✖️
prefer-object-has-own	Prefer Object.hasOwn() over Object.prototype.hasOwnProperty.call() and obj.hasOwnProperty()	✅	✅	✖️
prefer-spread-syntax	Prefer spread syntax over Array.concat(), Array.from(), Object.assign({}, ...), and Function.apply()	✅	✅	🔶
prefer-url-canparse	Prefer URL.canParse() over try-catch blocks for URL validation	✅	💡	✖️
prefer-get-or-insert	Prefer Map.prototype.getOrInsert() over reading a map entry with a default and writing it back	✖️	✅	✖️

Module replacements

Rule	Description	Recommended	Fixable	Requires Types
ban-dependencies	Disallow dependencies in favor of more performant or secure alternatives	✅	✖️	✖️

Performance improvements

Rule	Description	Recommended	Fixable	Requires Types
no-indexof-equality	Prefer startsWith() for strings and direct array access over indexOf() equality checks	✖️	✅	✅
prefer-array-from-map	Prefer Array.from(iterable, mapper) over [...iterable].map(mapper) to avoid intermediate array allocation	✅	✅	✖️
prefer-array-some	Prefer Array.some() over Array.find() and Array.filter().length checks when checking for element existence	✅	✅	✖️
prefer-timer-args	Prefer passing function and arguments directly to setTimeout/setInterval instead of wrapping in an arrow function or using bind	✅	✅	✖️
prefer-date-now	Prefer Date.now() over new Date().getTime() and +new Date()	✅	✅	✖️
prefer-regex-test	Prefer RegExp.test() over String.match() and RegExp.exec() when only checking for match existence	✅	✅	🔶
prefer-static-regex	Prefer defining regular expressions at module scope to avoid re-compilation on every function call	✅	✖️	🔶
prefer-inline-equality	Prefer inline equality checks over temporary object creation for simple comparisons	✖️	✅	🔶
prefer-string-fromcharcode	Prefer String.fromCharCode() over String.fromCodePoint() for code points below 0x10000	✅	✅	✖️
prefer-includes-over-regex-test	Prefer s.includes() / startsWith / endsWith over /literal/.test(s) when the regex has no metacharacters or flags	✖️	✅	✖️
prefer-charcode-at-in-loop	Prefer charCodeAt() over indexed string access for single-character comparisons inside loops	✖️	💡	🔶
prefer-throw-if-no-entry	Prefer {throwIfNoEntry: false} over relying on a thrown error for missing fs entries from sync stat calls	✖️	💡	✖️
no-delete-property	Disallow delete on properties — V8 deoptimizes the object to dictionary mode	✖️	💡	✖️
prefer-flatmap-over-map-flat	Prefer Array.prototype.flatMap() over .map(fn).flat() to skip the intermediate array	✖️	✅	✖️
prefer-slice-over-split-index	Prefer indexOf(needle) and slice(...) over split()[N] when splitting a string into two pieces	✖️	✖️	✖️
no-spread-in-reduce	Disallow spreading the accumulator inside a .reduce() callback — it's O(N²)	✖️	✖️	✖️
prefer-static-collator	Prefer hoisting an Intl.Collator over calling localeCompare inside a sort/toSorted callback	✖️	✖️	✖️

Sponsors

License

MIT