code: function stateStr(state) {
      if (state & STATE_CANCELLED) {
          return 'cancel';
      } else if (state & STATE_ENDED) {
          return 'end';
      } else if (state & STATE_CHANGED) {
          return 'move';
      } else if (state & STATE_BEGAN) {
          return 'start';
      }
      return '';
  }
docs: get a usable string, used as event postfix
  @param {Const} state
  @returns {String} state