But it doesn't really give a strong foundation on understanding the language. It's more like "I know mainstream C-inspired languages, and JS often burns me with its weird quirks like how the this keyword works, I just want to avoid getting burned". But it doesn't really embrace JS itself, just sort of acknowledges that you will be forced to use it in the web so you may as well at least learn the "good" parts.
It's still decent at that purpose, but for really strong competency in JS I can also vouch for the Eloquent JS book and the You Don't Know JS series (I've only read the first edition, a new edition is partially complete and available online).
I'm sure you know this, so I'm just pointing it out for completeness sake: that was indeed the only sensible approach to JavaScript back when that book was written.
ES6 and ES7 are widely supported now and are much better languages IMO.
Knowing the dead ends and the history behind them is nice, but I spent a lot of brain power on the dead ends that Eloquent put towards better use.
We're also talking a small book vs a tome of knowledge, but the philosophy is different regardless of size.
I've been wondering lately, as I'm moving (back) into a JavaScript-heavy stack (it's been... 4-5 years for me), is this book still relevant in the face of 12 years of JavaScript language development?