eslint

ESLint is the #1 JavaScript linter by downloads on npm (over 77M weekly downloads) and the most widely adopted pluggable linting utility for JavaScript and JSX. It helps you find and fix problems with your JavaScript code through static analysis.

Key features:

Static Code Analysis: Quickly finds problems in JavaScript code without executing it
Automatic Fixing: Many problems can be automatically fixed with syntax-aware corrections
Highly Configurable: Completely customizable rules, parsers, and plugins ecosystem
Built-in Editor Integration: Works seamlessly with most text editors
Extensible Plugin System: Thousands of community plugins for frameworks like React, Vue, Node.js
Multiple Output Formats: Supports various output formats including SARIF for security tools
Custom Rules: Write your own rules that work alongside ESLint's built-in rules

Common code quality checks:

Syntax Errors: Catches JavaScript syntax issues and typos
Code Style: Enforces consistent formatting, naming conventions, and code structure
Best Practices: Identifies problematic patterns and suggests improvements
Security Issues: Detects potential security vulnerabilities (with security plugins)
Performance: Identifies performance anti-patterns and optimizations

Popular configurations:

Airbnb Style Guide: Industry-standard JavaScript style guide
Standard: Minimal, opinionated code style with no configuration
Prettier Integration: Seamless integration with Prettier for code formatting

ESLint requires a custom configuration file applicable to your project. You can create it by typing npx eslint --init in the root of your repository.

Used by companies like Microsoft, Airbnb, Netflix, and Facebook, ESLint helps maintain code quality and consistency across JavaScript projects of all sizes.

ESLint v10 — resolving bare imports from `eslint.config.mjs`

ESLint v10 dropped support for the legacy .eslintrc.* format and only loads the new flat config (eslint.config.*). When MegaLinter runs ESLint from its own container install (/node-deps/node_modules) instead of your project's local node_modules, Node's ESM resolver may fail to locate bare imports such as import js from '@eslint/js' (upstream limitation tracked in eslint/eslint#18465), producing errors like:

Error [ERR_MODULE_NOT_FOUND]: Cannot find package '@eslint/js' imported from /github/workspace/eslint.config.mjs

Two recommended workarounds:

Workaround 1 — Use `createRequire` in `eslint.config.mjs`

Bare imports fall back to CommonJS resolution (which honors NODE_PATH and will pick up MegaLinter's bundled @eslint/js and related plugins):

import { createRequire } from 'module';
const require = createRequire(import.meta.url);
const js = require('@eslint/js');

Workaround 2 — Install dependencies in a pre-command and use the project-local ESLint binary

ESLint then runs from <workspace>/node_modules and resolves your config's imports naturally:

JAVASCRIPT_ES_PRE_COMMANDS:
  - command: yarn install --frozen-lockfile --ignore-scripts
    cwd: workspace
    continue_if_failed: false
JAVASCRIPT_ES_CLI_EXECUTABLE: node_modules/.bin/eslint

Replace yarn install --frozen-lockfile --ignore-scripts with npm ci (or npm install --include=dev) if your project uses npm.

eslint documentation

Version in MegaLinter: 10.4.0
Visit Official Web Site
See How to configure eslint rules
See How to disable eslint rules in files
See How to ignore files and directories with eslint
See Index of problems detected by eslint

Configuration in MegaLinter

Enable eslint by adding JAVASCRIPT_ES in ENABLE_LINTERS variable
Disable eslint by adding JAVASCRIPT_ES in DISABLE_LINTERS variable

Enable autofixes by adding JAVASCRIPT_ES in APPLY_FIXES variable

Variable	Description	Default value
JAVASCRIPT_ES_ARGUMENTS	User custom arguments to add in linter CLI call Ex: `-s --foo "bar"`
JAVASCRIPT_ES_COMMAND_REMOVE_ARGUMENTS	User custom arguments to remove from command line before calling the linter Ex: `-s --foo "bar"`
JAVASCRIPT_ES_FILTER_REGEX_INCLUDE	Custom regex including filter Ex: `(src\\|lib)`	Include every file
JAVASCRIPT_ES_FILTER_REGEX_EXCLUDE	Custom regex excluding filter Ex: `(test\\|examples)`	Exclude no file
JAVASCRIPT_ES_CLI_LINT_MODE	Override default CLI lint mode - `file`: Calls the linter for each file - `list_of_files`: Call the linter with the list of files as argument - `project`: Call the linter from the root of the project	`list_of_files`
JAVASCRIPT_ES_FILE_EXTENSIONS	Allowed file extensions. `"*"` matches any extension, `""` matches empty extension. Empty list excludes all files Ex: `[".py", ""]`	`[".js", ".vue"]`
JAVASCRIPT_ES_FILE_NAMES_REGEX	File name regex filters. Regular expression list for filtering files by their base names using regex full match. Empty list includes all files Ex: `["Dockerfile(-.+)?", "Jenkinsfile"]`	Include every file
JAVASCRIPT_ES_PRE_COMMANDS	List of bash commands to run before the linter	None
JAVASCRIPT_ES_POST_COMMANDS	List of bash commands to run after the linter	None
JAVASCRIPT_ES_UNSECURED_ENV_VARIABLES	List of env variables explicitly not filtered before calling JAVASCRIPT_ES and its pre/post commands	None
JAVASCRIPT_ES_CONFIG_FILE	eslint configuration file name Use `LINTER_DEFAULT` to let the linter find it	`eslint.config.js`
JAVASCRIPT_ES_RULES_PATH	Path where to find linter configuration file	Workspace folder, then MegaLinter default rules
JAVASCRIPT_ES_DISABLE_ERRORS	Run linter but consider errors as warnings	`false`
JAVASCRIPT_ES_DISABLE_ERRORS_IF_LESS_THAN	Maximum number of errors allowed	`0`
JAVASCRIPT_ES_CLI_EXECUTABLE	Override CLI executable	`['eslint']`

IDE Integration

Use eslint in your favorite IDE to catch errors before MegaLinter !

IDE	Extension Name	Install
Brackets	brackets-eslint	Visit Web Site
Eclipse	Tern-Linter-ESLint	Visit Web Site
Emacs	flycheck	Visit Web Site
IDEA	ESLint Plugin
Sublime Text	SublimeLinter-eslint	Visit Web Site
vim	ale	Visit Web Site
vim	Syntastic	Visit Web Site
Visual Studio Code	vscode-eslint

MegaLinter Flavors

This linter is available in the following flavors

Flavor	Description	Embedded linters
all	Default MegaLinter Flavor	136
cupcake	MegaLinter for the most commonly used languages	92
dotnetweb	Optimized for C, C++, C# or VB based projects with JS/TS	76
javascript	Optimized for JAVASCRIPT or TYPESCRIPT based projects	62

Behind the scenes

How are identified applicable files

Activated only if one of these files is found: eslint.config.js, eslint.config.mjs, eslint.config.cjs, eslint.config.ts, eslint.config.mts, eslint.config.cts, .eslintrc.json, .eslintrc.yml, .eslintrc.yaml, .eslintrc.js, .eslintrc.cjs, package.json:eslintConfig
File extensions: .js, .vue

How the linting is performed

eslint is called once with the list of files as arguments (list_of_files CLI lint mode)

Example calls

eslint myfile.js

eslint -c eslint.config.js --no-ignore myfile.js

eslint --fix -c eslint.config.js --no-ignore myfile.js

Help content

eslint [options] file.js [file.js] [dir]

Basic configuration:
  --no-config-lookup               Disable look up for eslint.config.js
  -c, --config path::String        Use this configuration instead of eslint.config.js, eslint.config.mjs, or eslint.config.cjs
  --inspect-config                 Open the config inspector with the current configuration
  --ext [String]                   Specify additional file extensions to lint
  --global [String]                Define global variables
  --parser String                  Specify the parser to be used
  --parser-options Object          Specify parser options

Specify Rules and Plugins:
  --plugin [String]                Specify plugins
  --rule Object                    Specify rules

Fix Problems:
  --fix                            Automatically fix problems
  --fix-dry-run                    Automatically fix problems without saving the changes to the file system
  --fix-type Array                 Specify the types of fixes to apply (directive, problem, suggestion, layout)

Ignore Files:
  --no-ignore                      Disable use of ignore files and patterns
  --ignore-pattern [String]        Patterns of files to ignore

Use stdin:
  --stdin                          Lint code provided on <STDIN> - default: false
  --stdin-filename String          Specify filename to process STDIN as

Handle Warnings:
  --quiet                          Report errors only - default: false
  --max-warnings Int               Number of warnings to trigger nonzero exit code - default: -1

Output:
  -o, --output-file path::String   Specify file to write report to
  -f, --format String              Use a specific output format - default: stylish
  --color, --no-color              Force enabling/disabling of color

Inline configuration comments:
  --no-inline-config               Prevent comments from changing config or rules
  --report-unused-disable-directives  Adds reported errors for unused eslint-disable and eslint-enable directives
  --report-unused-disable-directives-severity String  Chooses severity level for reporting unused eslint-disable and eslint-enable directives - either: off, warn, error, 0, 1, or 2
  --report-unused-inline-configs String  Adds reported errors for unused eslint inline config comments - either: off, warn, error, 0, 1, or 2

Caching:
  --cache                          Only check changed files - default: false
  --cache-file path::String        Path to the cache file. Deprecated: use --cache-location - default: .eslintcache
  --cache-location path::String    Path to the cache file or directory
  --cache-strategy String          Strategy to use for detecting changed files in the cache - either: metadata or content - default: metadata

Suppressing Violations:
  --suppress-all                   Suppress all violations - default: false
  --suppress-rule [String]         Suppress specific rules
  --suppressions-location path::String  Specify the location of the suppressions file
  --prune-suppressions             Prune unused suppressions - default: false
  --pass-on-unpruned-suppressions  Ignore unused suppressions - default: false

Miscellaneous:
  --init                           Run config initialization wizard - default: false
  --env-info                       Output execution environment information - default: false
  --no-error-on-unmatched-pattern  Prevent errors when pattern is unmatched
  --exit-on-fatal-error            Exit with exit code 2 in case of fatal error - default: false
  --no-warn-ignored                Suppress warnings when the file list includes ignored files
  --pass-on-no-patterns            Exit with exit code 0 in case no file patterns are passed
  --debug                          Output debugging information
  -h, --help                       Show help
  -v, --version                    Output the version number
  --print-config path::String      Print the configuration for the given file
  --stats                          Add statistics to the lint report - default: false
  --flag [String]                  Enable a feature flag
  --mcp                            Start the ESLint MCP server
  --concurrency Int|String         Number of linting threads, auto to choose automatically, off for no multithreading - default: off

Installation on mega-linter Docker image

Dockerfile commands :

# renovate: datasource=npm depName=eslint
ARG NPM_ESLINT_VERSION=10.4.0
# renovate: datasource=npm depName=@eslint/js
ARG NPM_ESLINT_JS_VERSION=10.0.1
# renovate: datasource=npm depName=eslint-config-prettier
ARG NPM_ESLINT_CONFIG_PRETTIER_VERSION=10.1.8
# renovate: datasource=npm depName=eslint-plugin-import-x
ARG NPM_ESLINT_PLUGIN_IMPORT_X_VERSION=4.16.2
# renovate: datasource=npm depName=eslint-plugin-jest
ARG NPM_ESLINT_PLUGIN_JEST_VERSION=29.15.2
# renovate: datasource=npm depName=eslint-plugin-n
ARG NPM_ESLINT_PLUGIN_N_VERSION=18.0.1
# renovate: datasource=npm depName=eslint-plugin-prettier
ARG NPM_ESLINT_PLUGIN_PRETTIER_VERSION=5.5.5
# renovate: datasource=npm depName=eslint-plugin-promise
ARG NPM_ESLINT_PLUGIN_PROMISE_VERSION=7.3.0
# renovate: datasource=npm depName=eslint-plugin-vue
ARG NPM_ESLINT_PLUGIN_VUE_VERSION=10.9.1
# renovate: datasource=npm depName=@microsoft/eslint-formatter-sarif
ARG NPM_MICROSOFT_ESLINT_FORMATTER_SARIF_VERSION=3.1.0

NPM packages (node.js):

Known errors and resolutions

When this linter fails for a known non-lint reason (remote service unavailable, malformed config, missing credentials, etc.), MegaLinter detects the pattern below in the linter output and surfaces the matching guidance.