eslint is the de facto standard for Javascript, there may be rules or plugins to check for date formatting rules.

There is no date formatting in JavaScript's standard library. External libraries tend to just fix this kind of thing with a breaking change.

There is – here’s the spec: https://tc39.es/ecma402/#datetimeformat-objects

Ah yes. I can't use that yet due to lack of browser support so I forgot it existed.

It’s pretty well supported now – even Internet Explorer 11 has partial support. But if you need it, there’s a polyfill here: https://formatjs.io/docs/polyfills/intl-datetimeformat/

There is Pylint for Python