code: function(callback){
          var that = this;
          var tickObj = {
              tick:function(dt){
                  that.removeTick(tickObj);
                  callback();
              }
          };
  
          that.addTick(tickObj);
          return tickObj;
      }
docs: 下次tick时回调
  @param  {Function} callback
  @return {tickObj}