All the functions, methods etc

Question

I learn js. In C/C++ we include a header file with all the functions we need. If you need to know how function works you can always look at "pure" description of it in header file. But I don't understand how it works in js.
And can you give me a link to some documentation of basic functions? (I mean such as slice, splice, reduce, map etc)
UPD. I meant pure CODE of it, not description

Answer 1

You can find lots of information (most of the time including code) about web development on the developer.mozilla website here is a link to javascript references:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference