TypeScript: Return value of super() calls not used for `this`

If a constructor returns a value other than this, then in subclasses super() calls to that constructor should use the result as this in the subclass constructor.

I believe this is specified in 12.3.5.1, step 10 of SuperCall: http://www.ecma-international.org/ecma-262/6.0/index.html#sec-super-keyword

Getting this behavior correct is going to be very important for supporting Custom Elements, which takes advantage of this to initialize browser-allocated elements with user-written constructors. See https://w3c.github.io/webcomponents/spec/custom/#htmlelement-constructor

Note, Babel 6 implements this correctly.

TypeScript Version:

1.8.9

Code

class Foo {

  x : number;

  constructor() {
    return {
      x: 1,
    };
  }
}

class Bar extends Foo {

  y : number;

  constructor() {
    super();
    this.y = 2;
  }
}

let o = new Bar();
console.assert(o.x === 1 && o.y === 2);

Expected behavior:

No assertion error

The constructor for Bar should compile to this:

var Bar = (function (_super) {
    __extends(Bar, _super);
    function Bar() {
        var _this = _super.call(this);
        _this.x = 1;
        return _this;
    }
    return Bar;
}(Foo));

Actual behavior:

Assertion error

The constructor for Bar compiles to this:

var Bar = (function (_super) {
    __extends(Bar, _super);
    function Bar() {
        _super.call(this);
        this.x = 1;
    }
    return Bar;
}(Foo));