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 ouchend)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