Question

I was browsing the MDC Doc Center page on Closures. And it mentions the introduction of the let keyword but only for use with browsers running at least the 1.7 release.

So I looked on Wikipedia only to find that Safari and Chrome are on 1.5, while it seems every new release of Firefox has been using a newer release of JS.

Why is that?

Answer 1

Use <script language="javascript1.7"></script> for Chrome. Probably the same for Safari.

EDIT: It appears that while chrome does support at least some JS1.8 features, it does not support several 1.7 features, including let.

The most recent mention (9 days ago) on this from a V8 person is here:

https://groups.google.com/d/topic/v8-users/-wu2BBL54pA/discussion

Several features (let, modules, destructuring) seem interesting. What is V8’s take on these features? And what is V8’s general view on new features after EcmaScript5 ?

Was answered with:

As we are doing with ES5, we will follow the language evolution when new specs are ratified in the EcmaScript spec committees and browser vendors agree to implement them. For some of the features we might start experimenting before the spec is ratified.

-Mads Sig Ager from the chromium project

Which is probably as close as we can get to “why.”