ES6 doesn't need opt-in

Mark S. Miller erights at
Fri Jan 6 00:00:38 PST 2012

On Thu, Jan 5, 2012 at 11:47 PM, Allen Wirfs-Brock <allen at>wrote:

>     1) program using only ES3 features and no "use strict";
>     2) program using only ES5 strict features and saying "use strict";
>     3) program using ES6-only features.
> Do these three programs operate in three different modes? If not, do #1
> and #2 operate in the same mode, or do #2 and #3 operate in the same mode?
> It isn't about "modes".  #1 and #2 are ES5 programs and are processed as
> such (applying/not the appropriately strictness as per ES5) . #3 is an ES6
> program is processed as such (including using the strict semantics that are
> universal to ES6).

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?

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