Beautify
Code is sometimes ugly. You want to make it look pretty. JS-beautify is one such tool.
For PHP, JavaScript and CSS, PHP Code Sniffer (phpcs) and its counterpart PHP Code Beautifier (phpcbf) work to ensure your code adheres to standards. For using phpcs in MediaWiki, see mw:Manual:Coding_conventions/PHP. PHPCS is enabled in ~89% of repositories hosted by WMF[1] MediaWiki Code Sniffer is the set of rules (or ruleset to be more precise) that defines the standards for the MediaWiki project.
Suffice it to say, you can composer phpcs to run the tool from the project root. For more on how to run it, see mw:Continuous_integration/PHP_CodeSniffer
Project Documentation for PHP_CodeSniffer is at https://github.com/PHPCSStandards/PHP_CodeSniffer/wiki
You can list the standards available in the MediaWiki project using the -i option. The standard you want to enforce/use is 'MediaWiki'
php ./vendor/bin/phpcs -i
The installed coding standards are MySource, PEAR, PSR1, PSR2, PSR12, Squiz, Zend, MediaWiki, Modernize, NormalizedArrays, Universal and PHPCSUtils
Configuration[edit]
If you're a MediaWiki extension developer, you can create a .phpcs.xml configuration file that sets things up for the project and integrates with the MediaWiki vendored binaries. See using docker-compose-ci