Announcement: ECMScript 4 to ECMAScript 3 translator released

Olav Kjær olav at
Mon Jun 9 10:21:20 PDT 2008

Hi everyone,

I have released Mascara version 0.1, an ECMAScript 4 to ECMAScript 3
compiler. <>

The code is still alpha-quality, but since it to a certain extend could be
regarded as an independent ES4 implementation, I thought it would be
relevant to announce on this mailing list.

There is an online interface <> where you can try it
out without installing anything.

Since comments on the implementation probably aren't appropriate for this
list, you are welcome to mail me directly, or to comment on the blog <> which I have set up for tracking the project.

While the implementation will probably never be a complete to-the-letter
implementation of the ES4 spec (e.g. the type checking is static - with
erasure - rather than runtime, and some features like metaprogramming and
generators are impractical to implement without support in the target
engine), I do believe it could be useful for raising awareness of ECMAScript
4 among web developers and to show that the language works in "the real

I suspect many developers are wary of investing in a technology which might
not be supported by IE without 3-party plug-in. And even if IE decide to
support ES4 natively, it would take years to reach ubiquitous support, which
is required for mainstream acceptance. The translator-approach shows a
viable migration path, where developers can start using ES4-constructs
today, without abandoning browser compatibility.

(Note: I actually started the project several years ago, based on the now
obsolete Netscape draft. However the current version is updated to support
the current spec as far as I can follow it on the wiki.)


Olav Junker Kjær
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