[ciw1973]

"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.