Fixing `Promise.resolve()`

C. Scott Ananian ecmascript at cscott.net
Wed Jun 10 15:44:51 UTC 2015


I don't agree that @@species is useful at all for changing constructor
signatures, since there is no closure argument.

If we had dynamically scoped variables, then:
```
  LabelledPromise[Symbol.species] = function() { return
LabelledPromise.bind(label/*dynamically scoped*/); };
  function() {
    let label = "foo";
    return LabelledPromise.resolve(x);
  }
```
would indeed be very interesting.  But in the absence of some sort of
closure, the only way you can make @@species into a custom constructor is
for odd special cases where you are just rearranging deck chairs.

Why not:
 ```
class LabelledPromise {
  constructor(exec, label) {
    super(exec);
    this.label = label === undefined ? "<derived promise>" : label;
  }
}
```
  --scott
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