Forwards-compatible syntax proposal

Mike Shaver mike.shaver at
Mon May 26 07:22:46 PDT 2008

On Mon, May 26, 2008 at 10:07 AM, Nathan de Vries <nathan at> wrote:
> On 26/05/2008, at 11:45 PM, Mike Shaver wrote:
> By "should work" I'm hoping you mean "will work", because that's the
> crux of what I'm asking :).

I mean "will work if correctly implemented, if there are not remaining
related bugs in the spec", but yeah.

> The main reason I'm interested in an ES4 script accessing an ES3
> script (I presume the the reverse is not possible?)

The reverse is indeed possible.

> is that all of my
> library code is ES3, and I'd like to be able to leave it as-is while
> I make the switch to ES4. A simple example would be the ability to
> use an ES3 library like Prototype.js from an ES4 script.

Yep, that's a critical use-case.

> If I needed to pull all ES3 code into an ES4 script tag - and make
> the bare-minimum changes - to be able to use that code in an ES4
> codebase, I (and I think many others) would be a sad panda indeed. Is
> behaviour like this expected to be defined in the ES spec, or is it
> open to vendor interpretation?

Interoperating with ES3 script, bidirectionally, is a big part of the
motivation for the details of the type system and other parts of the
language.  If there is an interoperability issue that's
underspecified, I think it's just a bug in the spec, and we should fix
it.  Early implementations shipped to millions of web users will help
identify them, as they have with various smaller changes already.


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