I’m quite the fan of the Syncfusion company. They publish a series of free e-books on technical topics. One of the new titles is “ECMAScript 6 Succinctly” by Matthew Duffield. See: https://www.syncfusion.com/resources/techportal/ebooks.
So what’s the catch? There isn’t any. I was skeptical when I first learned about Syncfusion. You have to give an e-mail address to get a free e-book, but Syncfusion keeps their messaging down to a reasonable level, and in fact, I find a lot of their messages interesting even if they are aimed at product of some sort.
I was the tech reviewer for the book, so I know it’s technically sound. The author, Matt, does a nice job of organizing and presenting a lot of information in just about 100 pages. “ECMAScript 6 Succinctly” by Matthew Duffield – highly recommended (and free!)