How do JavaScript versions correlate to ECMAScript versions?

Question

For example, [].map was "implemented in JavaScript 1.6." Is that an ES5 method? How does the 1.6 correlate to an ECMAScript version?

Answer 1

There aren't really strict correspondences between the version numbers Mozilla uses and the ECMAScript standard's version numbers. There's a table on Wikipedia that might be what you're looking for -- you'll see that JavaScript 1.6 corresponds to ECMAScript 3 and then some additional extensions. [].map specifically was standardized in ECMAScript 5, but to my understanding, the feature was first introduced by Firefox before the ECMAScript 5 standard was even published. (Firefox 1.5 which included JavaScript 1.6 was released on November 29, 2005, and the standard appears to have been published in September 2009.)