TypeScript: Incorrect/overly strong `this` inference for POJOs

TypeScript Version:

nightly (1.9.0-dev.20160419)

Code

Ember.Object.extend({
  init() {
    this._super();
//  ^~~~ error TS2339: Property '_super' does not exist on type '{ init(): void; }'.
    ...
  }
});

Expected behavior:

this should be inferred as any

Actual behavior:

this is inferred to be { init(): void; }

---

This changed somewhere between typescript@1.9.0-dev.20160319 and typescript@1.9.0-dev.20160419. I believe it is unsafe to assume anything about the this on the “methods” on a POJO, as there are several common patterns in JavaScript that breaks this assumption (using POJOs as an “options” or “extensions” dictionary).