ECMAScript is standardized as ECMA-262, which has had a number of revisions over the years. A version is also standardized as ISO/IEC 16262, which can be found in a "free" version (downloadable from ISO at no charge, but which has all sorts of licensing conditions you have to click through, and in a locked-up PDF file) as well as a paywalled version (just why somebody would pay for a file that's available free is unlcear). The ECMA versions, on the other hand, are out on the web for free.
- ECMA-262 spec, 3rd edition, 1999
- ECMA-262 spec, final 3rd edition, 2000
- ECMA-262 spec, 5th edition, 2009
- ECMA-262 spec, version 5.1, 2011
- ISO/IEC 16262 2011