It is very difficult to have an "official" reference as long as there are implementations (in all browsers) and there is a specification (ECMAScript) but no conformance tests of implementations against the specifications.
Now though, we have the EMCAScript 5 conformance suite at http://es5conform.codeplex.com/ - and there seems some consensus that ECMAScript implementations will come closer together, making ECMAScript more likely to be the official reference for the language.
