message: Removed only the passed in handler
diff: @@ -12,7 +12,7 @@ var createBackHandler = () => {
  }
  var removeEventListener = (_, handler) => {
  if (listeners.indexOf(handler) !== -1)
  - listeners.splice(listeners.indexOf(handler));
  + listeners.splice(listeners.indexOf(handler), 1);
  }
  return {listeners, addEventListener, removeEventListener};
  }
  