You Don't Know JS

'You Don't Know JS' by Kyle Simpson. A series of books that are a must read for any JavaScript developer. They are available for free on GitHub or you can purchase a retail version. He's working on a second edition right now. https://github.com/getify/You-Dont-Know-JS

You don't know JS goes quite in depth into a variety of areas. Worth reading further down the road. https://github.com/getify/You-Dont-Know-JS

"Eloquent Javascript" (http://eloquentjavascript.net/) definitely gets my vote, as it starts with concepts that someone new to programming would need to understand before diving into the specifics of the language. Available to read online for free, although well worth spending money on a physical copy to thumb through, but it may be a little too slow to get going for someone who already has experience with other languages. For developers, I'd recommend Kyle Simpson's "You Don't Know JS" books, in particular "This & Object Prototypes", followed by "Scopes & Closures". Well written, with plenty of example code, these are deep dives into specific areas which make Javascript different/weird. They're available to read in his Github repo (https://github.com/getify/You-Dont-Know-JS), but consider buying them, as he deserves to get paid.

Secrets of the JavaScript Ninja, Second Edition along with You Don't Know JS are always my two recommendations. The two together shore up the weaknesses in the other.

I think it depends on your learning style & what you want to learn. http://jsbooks.revolunet.com/ is a great resource for free books. If you want to learn concepts, You Don't Know JS by Kyle Simpson is great. If you want to learn by doing, I would look away from books & more towards video based learning. It seems to have richer content in this style. Pluralsight, Frontend Masters, Egghead & Code School are all great. They also target different niches. If you're a complete beginner I suggest Code School. It does the best out of those at telling you where to start & what to learn next.

Depends on what your level is going in. For an absolute beginner, JavaScript and jQuery by Jon Duckett is extremely accessible. Sure, it covers jQuery but it's so well aimed at total beginners it's not a bad path. At the lower intermediate level, Eloquent JavaScript (mentioned elsewhere) is fantastic. At higher levels/if you know other languages and are comfortable learning new ones: Effective JavaScript, YDKJS, and Speaking JavaScript all fantastic and complement each other in various ways.

You don't know JS is a good book to start with and explains ES6 too. It is available for free on github so you can evaluate before buying. https://github.com/getify/You-Dont-Know-JS

You Don't Know JS by Kyle Simpson is essential if you want to learn Javascript in depth.

The "You Don't Know JS" series was a real eye-opener for me.