ECMAScript Edition 4 and Backwards Compatibility

There's a new document on the incompatibilities between ECMAScript Edition 3 and the proposed Edition 4. Given the recent controversy in the blogosphere and the degree of interest in last week's discussion of the proposed ES4, this document may be of interest to LtUers.

It's also interesting to think of conservative extension not as an all-or-nothing property, but to judge incompatibilities in terms of their impact. This document attempts to enumerate and classify the different ways the proposed ES4 spec conflicts with the specification of ES3.

(One last note: there's a new pre-release of the reference implementation available, with binaries for all major platforms. Check it out!)

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Hi Dave, The reference

Hi Dave,

The reference implementation source file claims to be gzip'd tar file, but it's really just a tar file. You should make this consistent.


Whoops! Fixed, thanks.

Test drive

Breezing through the incompatibilities, I don't see any problems that will impact my code - so no complaints from this end. I downloaded the reference implementation and tested it against some of my code. On the negative side, parseFloat is not implemented yet. On the plus side, TCO works great.


The bug tracker is open to all comers. If you find bugs in the reference implementation and feel like contributing, do file them there.