Does Every Developer Know This MDN Trick? I Hope So.
mdn.io/thing in your browser bar, with "thing" being a keyword that would probably point to the documentation page you need.
This will run a search on MDN (Mozilla Developer Network) for a page that fits that "thing" you asked about and immediately take you to the page, much like Google's "I'm Feeling Lucky" button (which I used to thing was some kind of internet gambling button).
mdn.io/array takes you to the page about Array.prototype. That's not the actual url for that page, but what do you care! You got there none the less.
mdn.io/arrayslice takes you to a page defining the Array.prototype's slice method.
mdn.io/Mathfloor takes you to the page defining the floor method on the Math prototype.
Now there's no search at all. With mdn.io/ I feel like I have all the urls I need memorized.
MDN vs. W3 Schools
Plus MDN doesn't have any ads. So even though it is a little more intimidating than W3 Schools, do yourself a favor and start getting used to looking things up on MDN. Especially now that you know the mdn.io trick, you'll be glad you did.