深入浅出zeptojs中tap事件

1、tap事件实现

zepto 源码里面看关于tap的实现方法：

 $(document).ready(function(){
     var now, delta, deltaX = 0, deltaY = 0, firstTouch, _isPointerType

     if ('MSGesture' in window) {
       gesture = new MSGesture()
       gesture.target = document.body
     }

     $(document)
       .bind('MSGestureEnd', function(e){
         var swipeDirectionFromVelocity =
           e.velocityX > 1 ? 'Right' : e.velocityX < -1 ? 'Left' : e.velocityY > 1 ? 'Down' : e.velocityY < -1 ? 'Up' : null;
         if (swipeDirectionFromVelocity) {
           touch.el.trigger('swipe')
           touch.el.trigger('swipe'+ swipeDirectionFromVelocity)
         }
       })
       .on('touchstart MSPointerDown pointerdown', function(e){
         if((_isPointerType = isPointerEventType(e, 'down')) &&
           !isPrimaryTouch(e)) return
         firstTouch = _isPointerType ? e : e.touches[0]
         if (e.touches && e.touches.length === 1 && touch.x2) {
           // Clear out touch movement data if we have it sticking around
           // This can occur if touchcancel doesn't fire due to preventDefault, etc.
           touch.x2 = undefined
           touch.y2 = undefined
         }
         now = Date.now()
         delta = now - (touch.last || now)
         touch.el = $('tagName' in firstTouch.target ?
           firstTouch.target : firstTouch.target.parentNode)
         touchTimeout && clearTimeout(touchTimeout)
         touch.x1 = firstTouch.pageX
         touch.y1 = firstTouch.pageY
         if (delta > 0 && delta <= 250) touch.isDoubleTap = true
         touch.last = now
         longTapTimeout = setTimeout(longTap, longTapDelay)
         // adds the current touch contact for IE gesture recognition
         if (gesture && _isPointerType) gesture.addPointer(e.pointerId);
       })
       .on('touchmove MSPointerMove pointermove', function(e){
         if((_isPointerType = isPointerEventType(e, 'move')) &&
           !isPrimaryTouch(e)) return
         firstTouch = _isPointerType ? e : e.touches[0]
         cancelLongTap()
         touch.x2 = firstTouch.pageX
         touch.y2 = firstTouch.pageY

         deltaX += Math.abs(touch.x1 - touch.x2)
         deltaY += Math.abs(touch.y1 - touch.y2)
       })
       .on('touchend MSPointerUp pointerup', function(e){
         if((_isPointerType = isPointerEventType(e, 'up')) &&
           !isPrimaryTouch(e)) return
         cancelLongTap()

         // swipe
         if ((touch.x2 && Math.abs(touch.x1 - touch.x2) > 30) ||
             (touch.y2 && Math.abs(touch.y1 - touch.y2) > 30))

           swipeTimeout = setTimeout(function() {
             touch.el.trigger('swipe')
             touch.el.trigger('swipe' + (swipeDirection(touch.x1, touch.x2, touch.y1, touch.y2)))
             touch = {}
           }, 0)

         // normal tap
         else if ('last' in touch)
           // don't fire tap when delta position changed by more than 30 pixels,
           // for instance when moving to a point and back to origin
           if (deltaX < 30 && deltaY < 30) {
             // delay by one tick so we can cancel the 'tap' event if 'scroll' fires
             // ('tap' fires before 'scroll')
             tapTimeout = setTimeout(function() {

               // trigger universal 'tap' with the option to cancelTouch()
               // (cancelTouch cancels processing of single vs double taps for faster 'tap' response)
               var event = $.Event('tap')
               event.cancelTouch = cancelAll
               touch.el.trigger(event)

               // trigger double tap immediately
               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)
           } else {
             touch = {}
           }
           deltaX = deltaY = 0

       })
       // when the browser window loses focus,
       // for example when a modal dialog is shown,
       // cancel all ongoing events
       .on('touchcancel MSPointerCancel pointercancel', cancelAll)

     // scrolling the window indicates intention of the user
     // to scroll, not tap or swipe, so cancel all ongoing events
     $(window).on('scroll', cancelAll)
   })

   ;['swipe', 'swipeLeft', 'swipeRight', 'swipeUp', 'swipeDown',
     'doubleTap', 'tap', 'singleTap', 'longTap'].forEach(function(eventName){
     $.fn[eventName] = function(callback){ return this.on(eventName, callback) }
   })

zepto的tap通过兼听绑定在document上的touch事件来完成tap事件的模拟的,及tap事件是冒泡到document上触发的再点击完成时的tap事件(touchstart\touchend)需要冒泡到document上才会触发，而在冒泡到document之前，用户手的接触屏幕(touchstart)和离开屏幕(touchend)是会触发click事件的,因为click事件有延迟触发(这就是为什么移动端不用click而用tap的原因)(大概是300ms,为了实现safari的双击事件的设计)，所以在执行完tap事件之后，弹出来的选择组件马上就隐藏了，此时click事件还在延迟的300ms之中，当300ms到来的时候，click到的其实不是完成而是隐藏之后的下方的元素，如果正下方的元素绑定的有click事件此时便会触发，如果没有绑定click事件的话就当没click，但是正下方的是input输入框(或者select选择框或者单选复选框)，点击默认聚焦而弹出输入键盘，这就是常出现的“点透”的情况。

下面一个例子看看点透是什么情况：

 <!DOCTYPE html>
 <html>
 <head>
     <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
 <title></title>
     <style type="text/css">
         input {
             width: 200px;
             height: 50px;
         }
         .layer {
             width: 200px;
             height: 200px;
             position: absolute;
             left: 0;
             top: 0;
             background: red;
             opacity: .5;
         }
     </style>
 </head>
 <body>
 <div class="layer" id="J_layer"></div>
 <input type="text">

 <script type="text/javascript" src="/lib/zepto.js"></script>
 <script type="text/javascript">
     $('#J_layer').on('tap', function () {
         var $this = $(this);
         $this.hide();
     });
 </script>
 </body>
 </html>

运行出来的情况是：

当点击“layer”处于“input”上方区域后出现：

上图可以看出，input获取到了焦点。

这就是点透现象，input获取到了click事件。

 2、解决“点透”问题

2.1、引入fastclick.js，因为fastclick源码不依赖其他库所以你可以在原生的js前直接加上。https://github.com/ftlabs/fastclick

 window.addEventListener( "load", function() {
      FastClick.attach( document.body );
 }, false );

2.2、用touchend代替tap事件并阻止掉touchend的默认行为preventDefault()

 $("#layer").on("touchend", function (event) {
      //很多处理比如隐藏什么的
      event.preventDefault();
 });

2.3、延迟一定的时间(300ms+)来处理事件

 $("#layer").on("tap", function (event) {
     setTimeout(function(){
     //程序处理
     },320);
 }); 

以上就是对zepto中tap方法的解说，请大家多多提问