Add CustomEvent to lib.d.ts Window interface and global window object

mylib.d.ts

interface CustomEventParams {
    bubbles?: boolean;
    cancelable?: boolean;
    detail?: any;
}

// Extend the lib.d.ts CustomEvent interface with the proper constructor
interface CustomEvent {
    new(event: string, params?: CustomEventParams);
}

// Add the interface to the Window interface
interface Window {
    CustomEvent: CustomEvent;
}

polyfill.ts

(() => {
  function polyfill(pf: any) {
    window.CustomEvent = pf;
  }
  polyfill((event, params) => {
    params = params || { bubbles: false, cancelable: false, detail: undefined };
    var evt = <CustomEvent>document.createEvent('CustomEvent');
    evt.initCustomEvent(event, params.bubbles, params.cancelable, params.detail);
    return evt;
  });
})();

use.ts

window.dispatchEvent(new window.CustomEvent('Singularity'));

How do I import a self-executing function like this polyfill.ts to my main.ts?