We all know ECMAScript 6 was released in June 2015. Many new features made part of final edition of it. Work on ECMAScript 7 has started now.
Browsers are trst to implement these features assp.
has good updates on where browsers stand. So far IE11 seems to be leading this race, followed by Chrome.
All web developers must read the ECMAScript specifications at: http://www.ecma-international.org/ecma-262/6.0/