Exploring ES6: Upgrade to the next version of JavaScript

You are reading a book about ECMAScript 6 (ES6), a new version of JavaScript. It’s great that we can finally use that version, which had a long and eventful past: It was first conceived as ECMAScript 4, a successor to ECMAScript 3 (whose release was in December 1999). In July 2008, plans changed and the next versions of JavaScript were to be first a small incremental release (which became ES5) and then a larger, more powerful release. The latter had the code name Harmony and part of it became ES6.