Re: Subclassing ES6 objects with ES5 syntax.

[Alex Kocharin]

 

I believe you can subclass anything using code like this:

 

function MyPromise(executor) {

  var self = new Promise(executor)

  self.setPrototypeOf(self, MyPromise.prototype)

  return self

}

Object.setPrototypeOf(MyPromise, Promise)

 

 

... and it can be easily subclassed itself in the same way.

 

 

24.04.2015, 04:02, "C. Scott Ananian" <ecmascr...@cscott.net>:

Is there any way to access `new.target` using ES5 syntax?

It appears that the "correct" way to create a subclass using ES5 syntax is:
```
function MyPromise(executor) {
  var self = Reflect.construct(Promise, [executor], new.target);
  return self;
}
Object.setPrototypeOf(MyPromise, Promise);
```
But since `new.target` isn't accessible, we have to do something like:
```
function MyPromise(executor) {
  var self = Reflect.construct(Promise, [executor], MyPromise); // <-- THIS
  return self;
}
Object.setPrototypeOf(MyPromise, Promise);
```
which works for only a single level of subclassing.  That is, it allows us to create and instantiate MyPromise, but now nobody can subclass MyPromise.  That's too bad.

Is there any way around this?
  --scott

ps. Use case: My `prfun` package on npm subclasses `Promise` in order to add all the useful utility helpers without stomping on the global `Promise` object.  I'd like to do so in a way which is compatible with both native ES6 promises (if they are available) and properly-written ES5 shims.

,

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