Konami Code detector written in effection

konami.ts

import { run } from 'effection';
import { once } from '@effection/events';

run(function*() {
  yield konamiCodeEntered();
  alert('99 lives!');
});

function * konamiCodeEntered() {
  while (true) {
    if (yield nextKeyIs('ArrowUp')) {
      if (yield nextKeyIs('ArrowUp')) {
        if (yield nextKeyIs('ArrowDown')) {
          if (yield nextKeyIs('ArrowDown')) {
            if (yield nextKeyIs('ArrowLeft')) {
              if (yield nextKeyIs('ArrowRight')) {
                if (yield nextKeyIs('ArrowLeft')) {
                  if (yield nextKeyIs('ArrowRight')) {
                    if (yield nextKeyIs('b')) {
                      if (yield nextKeyIs('a')) {
                        if (yield nextKeyIs('b')) {
                          if (yield nextKeyIs('a')) {
                            return;
                          }
                        }
                      }
                    }
                  }
                }
              }
            }
          }
        }
      }
    }
  }
}

function* nextKeyIs(key: string) {
  let [event]: [KeyboardEvent] = yield once(document, 'keydown');
  return event.key === key
}