In what year was ECMAScript 6 finalized?

ECMAScript 6 was finalized in 2015.

The sixth edition of the ECMAScript standard was formally adopted by Ecma International’s General Assembly on June 17, 2015. It was published as ECMAScript 2015, establishing the naming pattern in which the edition number and year are both used: ES6 and ES2015 refer to the same major release.

The edition was unusually ambitious. Its features included let and const, arrow functions, classes, modules, promises, generators, iterators, destructuring, template literals, Maps, Sets, and symbols. Development had begun years earlier, with the sixth edition’s focused work starting in 2009.

A common mistake is to call 2016 the finalization year because ES2016 followed it. ES2016 was the seventh edition and introduced a smaller set of additions, including the exponentiation operator and Array.prototype.includes(). After ES2015, ECMAScript moved toward regular yearly editions rather than infrequent large revisions.