Despite being on top of Google’s Search Ranking, W3Schools apparently isn’t all that great. My co-worker showed me this interesting site, W3Fools, which is attempting to correct the many and many mistakes that W3School makes. It’s a great read. Especially if you are new to the Web world or have been only relying on W3Schools, it is a MUST read.
Personally, I’ve been using MDN mainly because it looks nicer and has more details about each function. It lacks great examples but those are easy to find in StackOverflow anyway. If you like more detail, up-to-date and visually-pleasant page to read, I really recommend it.