MDN Web Docs (formerly known as the Mozilla Developer Network or MDN) is a free resource for in-depth documentation on web standards such as HTML5, CSS, JavaScript, and much more.

MDN's mission is simple: provide developers with the information they need to easily build projects on the open Web. If it's an open technology exposed to the Web, we want to document it.

MDN Web Docs mission statement

A community of developers and other contributors keep the MDN Web Docs up-to-date. The entire site is a wiki, meaning anyone can add to or edit the growing collection of documentation and tutorials.

But you don't need to be a professional developer to contribute to MDN Web Docs! Like many other open source projects, there are a lot of ways you can help.

If you're interested in contributing to MDN Web Docs, check out their Getting Started page.

Here are some quick links to useful resources:

How to Use MDN Web Docs

MDN have built a reputation for having some of the best documentation for common web technologies. If you've ever been asked, "Have you checked the docs?" chances they're referring to MDN Web Docs.

Say you're working on a project and you want to use JavaScript's map() method, but you forgot the exact syntax.

All you need to do is pull up the page for map() and scroll down to the Syntax section.

There you'll get a quick overview of the syntax:

let new_array = callback( currentValue[, index[, array]]) {
    // return element for new_array
}[, thisArg])

And a list of arguments that the method accepts, along with a short description of each.

If you want to see some basic examples and common use cases, scroll down a bit more to the Examples section. There's a good chance that you'll find a snippet that you can use in your own project.

Also, if you ever find yourself having to support older browsers, most if not all the JavaScript documentation includes a Polyfill section.