最近看touch.js源码。发现

tapTimeout = setTimeout(function() {
              // trigger universal 'tap' with the option to cancelTouch()
              // (cancelTouch cancels processing of single vs double taps for faster 'tap' response)
              //直接触发tap事件。
              var event = $.Event('tap')
              event.cancelTouch = cancelAll
              //清空所有定时器以及 清空touch对象。
              touch.el.trigger(event)
              // trigger double tap immediately  立即触发双击事件。
              if (touch.isDoubleTap) {
                if (touch.el) touch.el.trigger('doubleTap')
                touch = {}
              }

              // trigger single tap after 250ms of inactivity
              else {
                touchTimeout = setTimeout(function(){
                  touchTimeout = null
                  if (touch.el) touch.el.trigger('singleTap')
                  touch = {}
                }, 250)
              }
            }, 0)
          }

想知道，tapTimeout存在的意义，是在主干进程中，提出此回调函数，方便其他条件判断是否取消此定时器？