On 02/25/11 13:26, Brendan Eich wrote:
On Feb 25, 2011, at 1:12 PM, Boris Zbarsky wrote:
On 2/25/11 4:08 PM, David Bruant wrote:
I would tend to be more in favor of disallowing Harmony features in
non-strict code (without explicit "use strict" directive) to avoid
surprises (I'm nuancing below).
I was under the impression that Harmony features would only be allowed for scripts
that opt in to them (via the type or language of the<script> tag or whatnot).
Does that alleviate this concern?
Yes, Harmony requires opt-in versioning, at least via<script
type="application/ecmascript;version=6"> (for example). An in-language "use version
6" pragma has been discussed too, for fail-fast when code gets copied and pasted into the wrong
container.
However, some cats are (at least partly) out of the bag in Firefox: let, const, yield.
Both let and yield require different opt-in already
(type="application/javascript;version=1.7").
Our let and const (especially) implementations are not Harmonious, and we still
need to pin down precise semantics for Harmony, but they are close enough --
see Waldemar's post:
http://www.mail-archive.com/[email protected]/msg05017.html -- and
generally used correctly (in future-proof ways) by their fans.
We at Mozilla will bear the cost of shifting (mostly Firefox add-on) JS hackers
over across any changes that do break let-, const-, and yield-using code. IOW,
we renounce any potential de-facto standard in our let and const prototype
implementations. We will break ourselves, and first, so that other implemntors
don't have to reverse-engineer our prototypes (not that this is a credible
problem: cross-browser JS code cannot use 'let' at all, and 'const' is not
consistently implemented either).
The function-in-block semantics in Firefox are un-Harmonious enough that we ban
those in Firefox 4's strict mode implementation.
Anyone writing cross-browser code will want to opt into Harmony, to shield
downrev browsers from syntax errors.
/be
If we're saying that Harmony is strict-only, settable by a <script> tag, what will
indirect eval and the Function constructor do if the evaluated code doesn't start with a
"use strict" directive?
Waldemar
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