npm install --save-dev eslint-config-wikimedia

Then, configure ESLint with one or more .eslintrc.json files as appropriate.

Below are some potential recommended uses:

This config allows the latest supported ES version code (currently ES2019) and browser native functions. It will complain about ES2020+ code and language features. This target version updates over time following MediaWiki's compatibility. It also automatically applies the Vue plugin and Vue-specific rules to .vue files.

.eslintrc.json:

{
	"extends": "wikimedia/client"
}

If you want to explicitly allow ES2019 code only, you can use wikimedia/client/es2019 instead.

This config adds the jQuery $ global, and additional rules preventing the use of jQuery features which are deprecated, have performance issues, or have simple modern ES alternatives. .eslintrc.json:

{
	"extends": [
		"wikimedia/client",
		"wikimedia/jquery"
	]
}

Code that runs in MediaWiki can use this config. It enforces rules that are specific to the MediaWiki codebase (core and extensions), such as correct documentation of mw.message usage, and prohibiting self-closing tags in Vue templates. .eslintrc.json:

{
	"extends": [
		"wikimedia/client",
		"wikimedia/mediawiki"
	]
}

You can extend the above config by also adding a second .eslintrc.json file in your tests directory:

tests/qunit/.eslintrc.json:

{
	"extends": [
		"wikimedia/mediawiki/qunit"
	]
}

Or for standalone JavaScript libraries and Node.js projects:

tests/.eslintrc.json:

{
	"extends": [
		"wikimedia/qunit"
	]
}

The following config will the Mocha environment and some Mocha related rules:

tests/mocha/.eslintrc.json:

{
	"root": true,
	"extends": [
		"wikimedia/server",
		"wikimedia/mocha"
	]
}

The following config will enable WDIO globals, as well as the Mocha and server configs:

tests/selenium/.eslintrc.json:

{
	"root": true,
	"extends": [
		"wikimedia/selenium"
	]
}

This config allows ES2018 code and Node native functions (i.e., Node 10.x). It will complain about ES2019+ code and language features.

.eslintrc.json:

{
	"extends": "wikimedia/server"
}

The wikimedia/server config consists of wikimedia, wikimedia/node and wikimedia/language/es2018. To use later versions of ES, for example ES2019, you can use the following config: .eslintrc.json:

{
	"extends": [
		"wikimedia",
		"wikimedia/node",
		"wikimedia/language/es2019"
	]
}

TypeScript cannot be directly handled by the browser (or ResourceLoader), so it will always target either code that runs on the server or tests or code that is compiled to JavaScript first in a non-MediaWiki step. TypeScript files are automatically included, similar to JSON and YAML files.

Please note that the basic project configuration does not specify any language or environmental defaults, and is unlikely to be suitable. However, if you wish to target clients with ES3 language support, or earlier versions of Node, this is a good place from which to start.

.eslintrc.json:

{
	"extends": "wikimedia"
}

All of the above configs are also available as flat config, for use with ESLint 9 or ESLint 8.57+. Pass the same names as you would use in extends, without the wikimedia/ prefix.

eslint.config.js:

const wikimedia = require( 'eslint-config-wikimedia/flat' );

module.exports = [
	...wikimedia( 'client', 'jquery', 'mediawiki' )
];

Major changes should be discussed on mediawiki.org or on the Wikitech mailing list beforehand.

Same approach as in ESLint, see https://github.com/eslint/eslint#user-content-semantic-versioning-policy.