anchor.diff: +import 'dart:async';
   import 'dart:html';
   import 'dart:math';
   import 'dart:collection';
  
positive.code: 
    Keyboard() {
      window.onKeyDown.listen((KeyboardEvent event) {
        if (!_keys.containsKey(event.keyCode)) {
          _keys[event.keyCode] = event.timeStamp;
        }
      });
  
      window.onKeyUp.listen((KeyboardEvent event) {
  
negative.code:     }
    }
  
    Future run() async {
      update(await window.animationFrame);
    }
  
    void update(num delta) {
  