ES6 doesn't need opt-in

Mark S. Miller erights at
Wed Jan 4 16:12:58 PST 2012

On Wed, Jan 4, 2012 at 1:07 PM, Brendan Eich <brendan at> wrote:

> See above. Function is implicitly strict.

I looked about and didn't see whatever I was supposed to notice.

I would *love* for Function to be implicitly strict. But I have no idea how
to do that without breaking the web. Function is a value on the heap shared
by legacy non-strict scripts and newfangled Harmony strict scripts. So far
we've been careful that the opt-in switches only per-code properties, not
per-heap properties. How would this work.

> We need a normative spec, of course! But we do not need to support new
> features in pre-strict-mode, indeed pre-ES6, combinations. New syntax is
> the opt-in!

If all new syntax causes opt-in, that does effectively bar non-strict mode
from being extended with non-strict versions of these primitives. That's a
fine outcome, but I'm surprised to hear it.

The problem I see is that the occurrence of some of these new features,
like a light use of destructuring, may not be notationally obvious to

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