On Sat, Feb 15, 2014 at 3:17 AM, Anne van Kesteren <[email protected]> wrote:
> It will take a long time before browsers support subclassing in
> general as far as I can tell.
I'm not talking about the class system in general. I'm talking about
the ES5+ code:
```js
Promise.prototype.bind = function(newThis) {
var SuperPromise = this._bindSuper || this.constructor || Promise;
// create a new Promise subclass (this is less cumbersome in es6, sigh)
var BoundPromise = function(exec) {
return SuperPromise.call(this, exec);
};
Object.setPrototypeOf(BoundPromise, SuperPromise);
BoundPromise.prototype = Object.create(SuperPromise.prototype);
BoundPromise.prototype.constructor = BoundPromise;
BoundPromise.prototype._bindSuper = SuperPromise;
BoundPromise.prototype.then = (function(superThen) {
return function(f, r) {
var ff = f && f.bind(newThis);
var rr = r && r.bind(newThis);
return superThen.call(this, ff, rr);
};
})(BoundPromise.prototype.then);
return newThis ? BoundPromise.resolve(this) : SuperPromise.resolve(this);
};
```
which is already useful in practice. It would be nice if the browsers
would support Promise subclassing of this sort, in the (long?) interim
without ES6 class syntax.
--scott
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