ES6 doesn't need opt-in

Axel Rauschmayer axel at
Thu Jan 5 08:30:07 PST 2012

On Jan 5, 2012, at 1:56 , Brendan Eich wrote:

> Better to dispense with modes or ordered versions altogether, which is the key idea of the proposal.

So, simplified, the story is:

- ES6 is a superset of ES5.strict.
- Therefore, as soon as we have ES6, ES5.strict code bases automatically become ES6 code bases.
- ES{3,5}.non-strict is neither a subset nor a superset of ES6, it has to be handled differently.

If these modes (strict versus non-strict) exist, then I would want a per-file marker for strict code:
- "use strict";
- use strict;
- module {

Compared to languages such as Java, JavaScript additionally faces the challenge that a developer can’t control what language version is implemented by the browser. How will that be handled? Sketching a solution would provide a more complete picture of how to migrate to ES6.

Dr. Axel Rauschmayer
axel at


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