Javascript support beyond 1.5. Why is it not there yet? [closed]

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Javascript 1.6 has been available since 2005 (in FF 2.0). Since then we have had quite a few new versions with new features. (Like v1.8.5, only supported in IE9 and FF4.)

Chrome, Opera and others seem to pride themselves by being up to date with the standards; can anybody provide resources or an idea why they have not yet "caught up"?

Built-in array extras and having let/yield would be quite nice.

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JavaScript versions are Firefox only code. And it's a proprietary extension that SHOULD NOT go into JavaScript.

Go read the Ecmascript 5 specification and see what's actually in the language.

ES5 support table

This question is equivalent to

IE has been supporting .htc files since 2000 why havn't Chrome, safari, firefox and opera started supporting them?