TypeScript type definitions for Event and EventTarget

[harmony7]

Adding type declarations for Event and EventTarget

So now you can do this:

  const eventTargetTest = new Promise<string>(resolve => {

    class FooEvent extends Event {
      constructor(value: string) {
        super('foo');
        this.value = value;
      }
      readonly value: string;
    }

    const eventTarget = new EventTarget();
    eventTarget.addEventListener('foo', (event) => {
      resolve((event as FooEvent).value);
    });

    setTimeout(() => {

      eventTarget.dispatchEvent(new FooEvent('event-target-test'));

    }, 1000);

  });
  const eventTargetTestValue = await eventTargetTest;