>> Ok, is there any observable difference between what you would have future
>> browsers do, vs the equivalent mechanisms except that program #2 is
>> categorized as an ES6 program and processed as such?
>>
>> If there is no observable difference, good. Then it's only a matter of how
>> we describe an agreed semantics. If there is an observable difference, how
>> is this not three modes?
>
> There should be no observable difference. But the issue isn't how we
> described the (program) semantics. It is how we decide which semantics to
> apply.
>
> The tricky cases are thing like:
>
> function f(a) {
> arguments[0]=2;
> return a
> }
> print(f(1)); //2 if ES5, 1 if ES6
>
> There is nothing in the source file that implies which specification to apply
> so for backwards computability a browser must default to interpreting such
> program as a ES5 program. Anything syntactically unique to ES5 (eg, use of a
> with statment) or ES6 (eg, use rest or spread) would force one interpretation
> or another
But what you are saying is that ES6 is not a superset of ES5.strict, right?
I thought that there were only 2 semantics:
1. ES5.non-strict (which is a superset of all previous versions) [a.k.a.
"non-strict"]
2. ES6 (which is a superset of ES5.strict) [a.k.a. "strict"]
My understanding is that #1 would be the default and when one encounters
anything ES6-specific (an “ES6 trigger”) or "use strict" then the semantics
switches to #2.
=> encountering a with statement would be fine, because #1 is the default,
anyway.
=> encountering a with statement and either an ES6 trigger or a "use strict"
would be an error.
As a human, I would want an ES6 trigger to appear as early as possible. I
wouldn’t want to read through a file, encounter an ES6 trigger at the end and
then have to revise the understanding of the code that I had so far. I like the
whole-file-or-nothing approach for switching semantics that you proposed.
--
Dr. Axel Rauschmayer
[email protected]
home: rauschma.de
twitter: twitter.com/rauschma
blog: 2ality.com
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