No more modes?

Brendan Eich brendan at mozilla.com
Thu Oct 14 13:48:19 PDT 2010


On Oct 14, 2010, at 1:39 PM, Jeff Walden wrote:

> On 10/14/2010 08:29 AM, Brendan Eich wrote:
>> Thus there is already one bit of opt-in versioning state in ES5, which must be carried from direct eval's caller to callee.
> 
> SpiderMonkey currently does this,

I wasn't describing any implementation, I was citing ES5 10.1.1, second bullet:

* Eval code is strict eval code if it begins with a Directive Prologue that contains a Use Strict Directive or if the call to eval is a direct call (see 15.1.2.1.1) to the eval function that is contained in strict mode code. 


> but fairly shortly (I have patches) it will not.  The eval *function*'s implementation will always perform indirect eval, and only the eval opcode will perform direct eval.  (We could statically distinguish strict+direct from non-strict+direct, too, with a separate opcode, but since it's trivial to query the currently executing script's strictness, runtime detection seems better than burning an opcode.)
> 
> That's only SpiderMonkey, of course, but as far as I can tell the concepts are applicable to any ECMAScript implementation.

This is an implementation detail, independent of ES5 10.1.1 and unobservable unless there's a bug.

/be

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