query.js

function query<T>(selector: string, klass: Class<T>): T {
  let element = document.querySelector(selector);

  if (!(element instanceof klass)) {
    throw new TypeError("expected " + selector + " to select element of type " + (klass : Function).name);
  }

  return element;
}

// legit:
let audio = query("audio", HTMLAudioElement);

// type error:
let audio: HTMLSpanElement = query("audio", HTMLAudioElement);
// 33:   let audio: HTMLSpanElement = query("audio", HTMLAudioElement);
//                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ HTMLAudioElement. This type is incompatible with
// 33:   let audio: HTMLSpanElement = query("audio", HTMLAudioElement);
//                  ^^^^^^^^^^^^^^^ HTMLSpanElement