On Feb 18, 2014, at 11:38 PM, C. Scott Ananian wrote: > [resending to list, original was sent from wrong address and got bounced] > > On Tue, Feb 18, 2014 at 11:12 AM, Allen Wirfs-Brock > <[email protected]> wrote: >> On Feb 18, 2014, at 12:44 PM, C. Scott Ananian wrote: >>> ```js >>> var SubPromise = function(exec) { Promise.call(this, exec); ... }; >>> Object.setPrototypeOf(SubPromise, Promise); >>> SubPromise.prototype = Object.create(Promise.prototype); >>> SubPromise.prototype.constructor = SubPromise; >>> ``` >>> Note that `SubPromise` inherits `Promise.@@create` and so this code >>> will work fine in an ES6 environment. (Blame @domenic, he showed me >>> that this should work!) > ... >> It wouldn't work in an implementation where Promise was natively implemented >> according to the ES6 Promise spec but where 'new SubPromise(exec)' did not >> include a call to SubPromise.@@create. > > ... > So the code above would work in a fully-compliant ES6 implementation. > The question is: what should it do in the weird "not quite ES6, but > more than ES5" implementations that are shipping today. This isn't an > ES6 spec issue, it's a challenge to implementors to provide > forward-compatibility.
Right, that's what I was trying to say. It all depends upon the new operator invoking @@create. It wouldn't work on an partial ES6 implementation where Promise.@@create was missing or where 'new' did not invoke @@create. Allen
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