Another crazy excellent (and free) ES6 reference is http://exploringjs.com/es6/ http://exploringjs.com/es6/ by Dr. Axel Rauschmayer - one of the ES6 committee m

Another crazy excellent (and free) ES6 reference is http://exploringjs.com/es6/ http://exploringjs.com/es6/ by Dr. Axel Rauschmayer - one of the ES6 committee members. JS is a very complicated language - and the language spec in written in a way - that while I am sure is excellent for implementors and compatibility - is pretty much unreadable by language users. Axel's book is quite authoritative and very readable. You may still go to the spec for finer points - but it sure is 10,000 times easier if you mostly understand the mechanism (and motivations) first.