eslint-plugin-regexp

What is eslint-plugin-regexp?

eslint-plugin-regexp is an ESLint plugin that provides linting rules for regular expressions. It helps developers write more efficient, readable, and secure regular expressions by catching common mistakes and suggesting improvements.

What are eslint-plugin-regexp's main functionalities?

No Unnecessary Escape

This rule disallows unnecessary escape characters in regular expressions. In the example, the backslash before the dot is unnecessary and should be removed.

/* eslint regexp/no-useless-escape: 'error' */
const regex = /\./;

No Obscure Character Class

This rule disallows obscure character class ranges that can be confusing or error-prone. In the example, the character class is clear and does not contain obscure ranges.

/* eslint regexp/no-obscure-range: 'error' */
const regex = /[a-zA-Z]/;

No Unnecessary Quantifier

This rule disallows unnecessary quantifiers in regular expressions. In the example, the quantifier {1} is unnecessary and should be removed.

/* eslint regexp/no-useless-quantifier: 'error' */
const regex = /a{1}/;

No Empty Character Class

This rule disallows empty character classes in regular expressions. In the example, the character class is empty and should be corrected.

/* eslint regexp/no-empty-character-class: 'error' */
const regex = /[]/;

Other packages similar to eslint-plugin-regexp

eslint-plugin-security

eslint-plugin-security is an ESLint plugin that helps identify potential security issues in JavaScript code. While it covers a broader range of security concerns, it includes some rules related to regular expressions, such as detecting potential ReDoS (Regular Expression Denial of Service) vulnerabilities. It is more general in scope compared to eslint-plugin-regexp.

eslint-plugin-unicorn

eslint-plugin-unicorn is a collection of various ESLint rules aimed at improving code quality and consistency. It includes some rules for regular expressions, such as preventing potential ReDoS attacks and suggesting more readable patterns. However, it is not as focused on regular expressions as eslint-plugin-regexp.

README

Introduction

eslint-plugin-regexp is ESLint plugin for finding RegExp mistakes and RegExp style guide violations.

:name_badge: Features

This ESLint plugin provides linting rules relate to better ways to help you avoid problems when using RegExp.

• Find the wrong usage of regular expressions, and their hints.
• Enforces a consistent style of regular expressions.
• Find hints for writing optimized regular expressions.
• 80 plugin rules for regular expression syntax and features.

You can check on the Online DEMO.

:book: Documentation

See documents.

:cd: Installation

npm install --save-dev eslint eslint-plugin-regexp

Requirements

• ESLint v8.44.0 and above
• Node.js v18.x, v20.x and above

:book: Usage

Add regexp to the plugins section of your eslint.config.js or .eslintrc configuration file (you can omit the eslint-plugin- prefix) and either use one of the two configurations available (recommended or all) or configure the rules you want:

The recommended configuration (New Config)

The plugin.configs["flat/recommended"] config enables a subset of the rules that should be most useful to most users. See lib/configs/rules/recommended.ts for more details.

// eslint.config.js
import * as regexpPlugin from "eslint-plugin-regexp"

export default [
    regexpPlugin.configs["flat/recommended"],
];

The recommended configuration (Legacy Config)

The plugin:regexp/recommended config enables a subset of the rules that should be most useful to most users. See lib/configs/rules/recommended.ts for more details.

// .eslintrc.js
module.exports = {
    "plugins": [
        "regexp"
    ],
    "extends": [
         // add more generic rulesets here, such as:
         // 'eslint:recommended',
        "plugin:regexp/recommended"
    ]
}

Advanced Configuration

Override/add specific rules configurations. See also: http://eslint.org/docs/user-guide/configuring.

// eslint.config.js
import * as regexpPlugin from "eslint-plugin-regexp"

export default [
    {
        plugins: { regexp: regexpPlugin },
        rules: {
            // Override/add rules settings here, such as:
            "regexp/rule-name": "error"
        }
    }
];

// .eslintrc.js
module.exports = {
    "plugins": [
        "regexp"
    ],
    "rules": {
        // Override/add rules settings here, such as:
        "regexp/rule-name": "error"
    }
}

Using the all configuration

The plugin.configs["flat/all"] / plugin:regexp/all config enables all rules. It's meant for testing, not for production use because it changes with every minor and major version of the plugin. Use it at your own risk. See lib/configs/rules/all.ts for more details.

:white_check_mark: Rules

💼 Configurations enabled in.
⚠️ Configurations set to warn in.
🟢 Set in the flat/recommended configuration.
🔵 Set in the recommended configuration.
🔧 Automatically fixable by the --fix CLI option.
💡 Manually fixable by editor suggestions.

Possible Errors

Name	Description	💼	⚠️	🔧	💡
no-contradiction-with-assertion	disallow elements that contradict assertions	🟢 🔵			💡
no-control-character	disallow control characters				💡
no-dupe-disjunctions	disallow duplicate disjunctions	🟢 🔵			💡
no-empty-alternative	disallow alternatives without elements		🟢 🔵		💡
no-empty-capturing-group	disallow capturing group that captures empty.	🟢 🔵
no-empty-character-class	disallow character classes that match no characters	🟢 🔵
no-empty-group	disallow empty group	🟢 🔵
no-empty-lookarounds-assertion	disallow empty lookahead assertion or empty lookbehind assertion	🟢 🔵
no-escape-backspace	disallow escape backspace ([\b])	🟢 🔵			💡
no-invalid-regexp	disallow invalid regular expression strings in RegExp constructors	🟢 🔵
no-lazy-ends	disallow lazy quantifiers at the end of an expression		🟢 🔵		💡
no-misleading-capturing-group	disallow capturing groups that do not behave as one would expect	🟢 🔵			💡
no-misleading-unicode-character	disallow multi-code-point characters in character classes and quantifiers	🟢 🔵		🔧	💡
no-missing-g-flag	disallow missing g flag in patterns used in String#matchAll and String#replaceAll	🟢 🔵		🔧
no-optional-assertion	disallow optional assertions	🟢 🔵
no-potentially-useless-backreference	disallow backreferences that reference a group that might not be matched		🟢 🔵
no-super-linear-backtracking	disallow exponential and polynomial backtracking	🟢 🔵		🔧
no-super-linear-move	disallow quantifiers that cause quadratic moves
no-useless-assertions	disallow assertions that are known to always accept (or reject)	🟢 🔵			💡
no-useless-backreference	disallow useless backreferences in regular expressions	🟢 🔵
no-useless-dollar-replacements	disallow useless $ replacements in replacement string	🟢 🔵
strict	disallow not strictly valid regular expressions	🟢 🔵		🔧	💡

Best Practices

Name	Description	💼	⚠️	🔧	💡
confusing-quantifier	disallow confusing quantifiers		🟢 🔵
control-character-escape	enforce consistent escaping of control characters	🟢 🔵		🔧
negation	enforce use of escapes on negation	🟢 🔵		🔧
no-dupe-characters-character-class	disallow duplicate characters in the RegExp character class	🟢 🔵		🔧
no-empty-string-literal	disallow empty string literals in character classes	🟢 🔵
no-extra-lookaround-assertions	disallow unnecessary nested lookaround assertions	🟢 🔵		🔧
no-invisible-character	disallow invisible raw character	🟢 🔵		🔧
no-legacy-features	disallow legacy RegExp features	🟢 🔵
no-non-standard-flag	disallow non-standard flags	🟢 🔵
no-obscure-range	disallow obscure character ranges	🟢 🔵
no-octal	disallow octal escape sequence				💡
no-standalone-backslash	disallow standalone backslashes (\)
no-trivially-nested-assertion	disallow trivially nested assertions	🟢 🔵		🔧
no-trivially-nested-quantifier	disallow nested quantifiers that can be rewritten as one quantifier	🟢 🔵		🔧
no-unused-capturing-group	disallow unused capturing group	🟢 🔵		🔧	💡
no-useless-character-class	disallow character class with one character	🟢 🔵		🔧
no-useless-flag	disallow unnecessary regex flags		🟢 🔵	🔧
no-useless-lazy	disallow unnecessarily non-greedy quantifiers	🟢 🔵		🔧
no-useless-quantifier	disallow quantifiers that can be removed	🟢 🔵		🔧	💡
no-useless-range	disallow unnecessary character ranges	🟢 🔵		🔧
no-useless-set-operand	disallow unnecessary elements in expression character classes	🟢 🔵		🔧
no-useless-string-literal	disallow string disjunction of single characters in \q{...}	🟢 🔵		🔧
no-useless-two-nums-quantifier	disallow unnecessary {n,m} quantifier	🟢 🔵		🔧
no-zero-quantifier	disallow quantifiers with a maximum of zero	🟢 🔵			💡
optimal-lookaround-quantifier	disallow the alternatives of lookarounds that end with a non-constant quantifier		🟢 🔵		💡
optimal-quantifier-concatenation	require optimal quantifiers for concatenated quantifiers	🟢 🔵		🔧
prefer-escape-replacement-dollar-char	enforces escape of replacement $ character ($$).
prefer-predefined-assertion	prefer predefined assertion over equivalent lookarounds	🟢 🔵		🔧
prefer-quantifier	enforce using quantifier			🔧
prefer-range	enforce using character class range	🟢 🔵		🔧
prefer-regexp-exec	enforce that RegExp#exec is used instead of String#match if no global flag is provided
prefer-regexp-test	enforce that RegExp#test is used instead of String#match and RegExp#exec			🔧
prefer-set-operation	prefer character class set operations instead of lookarounds	🟢 🔵		🔧
require-unicode-regexp	enforce the use of the u flag			🔧
require-unicode-sets-regexp	enforce the use of the v flag			🔧
simplify-set-operations	require simplify set operations	🟢 🔵		🔧
sort-alternatives	sort alternatives if order doesn't matter			🔧
use-ignore-case	use the i flag if it simplifies the pattern	🟢 🔵		🔧

Stylistic Issues

Name	Description	💼	⚠️	🔧	💡
grapheme-string-literal	enforce single grapheme in string literal
hexadecimal-escape	enforce consistent usage of hexadecimal escape			🔧
letter-case	enforce into your favorite case			🔧
match-any	enforce match any character style	🟢 🔵		🔧
no-useless-escape	disallow unnecessary escape characters in RegExp	🟢 🔵		🔧
no-useless-non-capturing-group	disallow unnecessary non-capturing group	🟢 🔵		🔧
prefer-character-class	enforce using character class	🟢 🔵		🔧
prefer-d	enforce using \d	🟢 🔵		🔧
prefer-lookaround	prefer lookarounds over capturing group that do not replace			🔧
prefer-named-backreference	enforce using named backreferences			🔧
prefer-named-capture-group	enforce using named capture groups
prefer-named-replacement	enforce using named replacement			🔧
prefer-plus-quantifier	enforce using + quantifier	🟢 🔵		🔧
prefer-question-quantifier	enforce using ? quantifier	🟢 🔵		🔧
prefer-result-array-groups	enforce using result array groups			🔧
prefer-star-quantifier	enforce using * quantifier	🟢 🔵		🔧
prefer-unicode-codepoint-escapes	enforce use of unicode codepoint escapes	🟢 🔵		🔧
prefer-w	enforce using \w	🟢 🔵		🔧
sort-character-class-elements	enforces elements order in character class			🔧
sort-flags	require regex flags to be sorted	🟢 🔵		🔧
unicode-escape	enforce consistent usage of unicode escape or unicode codepoint escape			🔧
unicode-property	enforce consistent naming of unicode properties			🔧

Removed

• :no_entry: These rules have been removed in a previous major release, after they have been deprecated for a while.

Rule ID	Replaced by	Removed in version
no-assertion-capturing-group	regexp/no-empty-capturing-group	v2.0.0
no-useless-exactly-quantifier	regexp/no-useless-quantifier, regexp/no-zero-quantifier	v2.0.0
no-useless-non-greedy	regexp/no-useless-lazy	v2.0.0
order-in-character-class	regexp/sort-character-class-elements	v2.0.0
prefer-t	regexp/control-character-escape	v2.0.0

:gear: Settings

See Settings.

:traffic_light: Semantic Versioning Policy

eslint-plugin-regexp follows Semantic Versioning and ESLint's Semantic Versioning Policy.

:beers: Contributing

Welcome contributing!

Please use GitHub's Issues/PRs.

See CONTRIBUTING.md.

Development Tools

• npm test runs tests and measures coverage.
• npm run update runs in order to update readme and recommended configuration.
• npm run new [new rule name] runs to create the files needed for the new rule.
• npm run docs:watch starts the website locally.

:lock: License

See the LICENSE file for license rights and limitations (MIT).

Changelog

2.7.0

Minor Changes

• Add support for ES2025 duplicate named capturing groups (#752)

Patch Changes

• Updates unicode property alias resource with latest (#766)

• fix(regexp/no-useless-dollar-replacements): Correct capturing group not found grammar (#776)