This article explains the effects of the new u flag for regular expressions in ES6.
ES6 updates the grammar for identifiers. This affects a number of things, but most importantly, identifiers can be used as variable names, and identifier names are valid unquoted property names. This post describes the observable changes compared to the old ES5 behavior.
This seems to be a very common misconception that just won’t die. I keep running into it in blog posts, Twitter discussions, and even books.