What are the version numbers of JavaScript and what ECMAScript version do they correspond to?

Question

I was looking up the history of JavaScript and found out that the ECMAScript specification is based on it. So JavaScript is older than ECMAScript but seems to have become an implementation of that specification later on.

So what I found out so far is that:

• JavaScript 1.0 was the first version
• ECMAScript 3 is implemented in JavaScript 1.5
• ECMAScript 4 was never completed
• ECMAScript 5 is implemented in JavaScript 1.8.5
• ECMAScript 6 was released 2015 (therefore it is also called ECMAScript 2015)
• ECMAScript 7 was released 2016 (therefore it is also called ECMAScript 2016)

After Version 1.8.5 of JavaScript I can't find any higher version numbers of it. Which versions of JavaScript implement ECMAScript 6 or 7?

Answer 1

According to Wikipedia, the JavaScript-specific version numbers were only used by Firefox, and were dropped in Firefox 4.

These days, there's not really such thing as 'the current version of JavaScript' - the ECMAScript standards get created, and the browser vendors implement the features into their JS engines at their own pace. This pace varies wildly - as demonstrated by the very useful Kangax compatibility table.

Answer 2

https://developer.mozilla.org/en-US/docs/Web/JavaScript/New_in_JavaScript#JavaScript_versions:

Deprecated. The explicit versioning and opt-in of language features was Mozilla-specific and is in process of being removed. Firefox 4 was the last version which referred to an JavaScript version (1.8.5). With new ECMA standards, JavaScript language features are now often mentioned with their initial definition in ECMA-262 Editions such as ECMAScript 2015.

Starting with Firefox 5, changes in JavaScript are listed at https://developer.mozilla.org/en-US/docs/Web/JavaScript/New_in_JavaScript/Firefox_JavaScript_changelog, but not versioned otherwise.

See the lists at ECMAScript 2015 support in Mozilla and ECMAScript Next support in Mozilla for which features are available in which version of Firefox.