Allow subclass constructors without super() call

TypeScript Version:

1.8.0

Code

Custom element classes often have constructors that just return document.createElement(), since HTMLElement doesn’t have a callable constructor, but this generates an error in TypeScript:

class MyElement extends HTMLElement {
  constructor() {
    return document.createElement('my-element');
  }
}

In general, it is completely valid ES2015 to not call super(), as long as you don’t access this.

[justinfagnani]

Apparently TS’s super() check isn’t too robust, so I just did this:

constructor() {
  if (1 < 0) { // edit, this used to be 1 < 0, @xLama is right :)
    super();
  }
  return document.createElement('my-element');
}

[DanielRosenwasser]

Given that HTMLElement’s constructor never actually returns, it should actually return never. I’m thinking that

1. It should be allowed to extend something which has a construct signature of type never.
2. If a construct signature of some value’s type returns never, then a super call is not needed if extending from that value.
3. If there is a super() call, it should be an error to access this before super (which is currently the case anyway).