I'm using MDN quite a lot. Explanations are sparse, useful examples rare, and there's an assumption of underlying familiarity with syntax that can make it pretty difficult to follow.

What is polyfill?

It's the thick paste you use on walls to smooth over cracks.

It's also when you re-implement native functionality from newer browsers in JavaScript for the benefit of older browsers - see for example the Array.prototype.map polyfill.

> Explanations are sparse

I prefer the term concise - no need to dredge through unnecessary waffle to figure out what something does.

> useful examples rare

Possibly. On most sites I tend towards going straight to the examples because the explanations are waffle, but don't need to with MDN.

> there's an assumption of underlying familiarity

That'll be because it's mostly a reference.

There is a JavaScript Guide which appears very comprehensive, but looking at a few pages it does a horrific job of explaining stuff and has some terrible examples, so, yeah... that sucks. :/