Zepto.js touch模块深入分析

源码：

//	 Zepto.js
//	 (c) 2010-2015 Thomas Fuchs
//	 Zepto.js may be freely distributed under the MIT license.

;
(function($) {
  var touch = {},
    touchTimeout, tapTimeout, swipeTimeout, longTapTimeout,
    longTapDelay = 750,
    gesture
    function swipeDirection(x1, x2, y1, y2) {
      return Math.abs(x1 - x2) >=
        Math.abs(y1 - y2) ? (x1 - x2 > 0 ? 'Left' : 'Right') : (y1 - y2 > 0 ? 'Up' : 'Down')
    }
    function longTap() {
      longTapTimeout = null
      if (touch.last) {
        touch.el.trigger('longTap')
        touch = {}
      }
    }
    function cancelLongTap() {
      if (longTapTimeout) clearTimeout(longTapTimeout)
      longTapTimeout = null
    }
    function cancelAll() {
      if (touchTimeout) clearTimeout(touchTimeout)
      if (tapTimeout) clearTimeout(tapTimeout)
      if (swipeTimeout) clearTimeout(swipeTimeout)
      if (longTapTimeout) clearTimeout(longTapTimeout)
      touchTimeout = tapTimeout = swipeTimeout = longTapTimeout = null
      touch = {}
    }
    function isPrimaryTouch(event) {
      return (event.pointerType == 'touch' ||
        event.pointerType == event.MSPOINTER_TYPE_TOUCH) && event.isPrimary
    }
    function isPointerEventType(e, type) {
      return (e.type == 'pointer' + type ||
        e.type.toLowerCase() == 'mspointer' + type)
    }
  $(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)

分析：

var now, delta, touch = {};
$(document)
    .on('touchstart', startListener)
    .on('touchmove', moveListener)
    .on('touchend', endListener);

1、是单击还是双击

function startListener(e){
  now = Date.now();
  delta = now - (touch.last || now);
  // 手指连续轻触两次，时间间隔大于0，小于等于.25s，则为双击，反之单击
  if ( delta > 0 && delta <= 250 ) {
    touch.isDoubleTap = true;
  }
  touch.last = now;
}

2、处理手指长按

var longTapTimeout, longTapDelay = 750;
function longTap() {
  longTapTimeout = null
  if (touch.last) {
    touch.el.trigger('longTap')
    touch = {}
  }
}
function cancelLongTap() {
  if (longTapTimeout) clearTimeout(longTapTimeout)
  longTapTimeout = null
}
function startListener(e){
  // 默认就是长按，如果手指未移动和离开，超过.75s就触发longTap
  longTapTimeout = setTimeout(longTap, longTapDelay)
}
function moveListener(e){
  // 如果手指轻触屏幕后未超过.75s，则取消手指长按监听
  longTapTimeout = setTimeout(longTap, longTapDelay)
}
function endListener(e){
  // 如果手指轻触屏幕后未超过.75s，则取消手指长按监听
  longTapTimeout = setTimeout(longTap, longTapDelay)
}

3、是滑动(swipe)还是轻触(tap)

// 如果手指移动屏幕超过30像素，则触发相应的滑动事件，swipeLeft, swipeRight, swipeUp, swipeDown
function endListener(e){
  // 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);
  }
  else {
    // handle tap
    // 关于处理tap事件，请看第四点
  }
}

4、轻触 tap, singleTap, doubleTap 4.1、何时触发 tap ？

条件1：手指移动不超过30像素

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

条件2：依据条件1，基本上可以触发tap了，但是还考虑了另一种情况，手指滑动屏幕后又滑动到起始点，那么：

!Math.abs(touch.x1 - touch.x2) > 30) === !Math.abs(touch.y1 - touch.y2) > 30) === true;

为了不触发tap事件，这里又加了条件限制，理解这点很重要

if (deltaX < 30 && deltaY < 30) {
    // handle tap
}

注意：

deltaX !== Math.abs(touch.x1 - touch.x2);
deltaY !== Math.abs(touch.y1 - touch.y2);

请看 moveListener 中的代码：

function moveListener(e){
  // ...
  touch.x2 = firstTouch.pageX
  touch.y2 = firstTouch.pageY
  deltaX += Math.abs(touch.x1 - touch.x2)
  deltaY += Math.abs(touch.y1 - touch.y2)
}

例: deltaX的计算，你懂得...

if ( Math.abs(touch.x1 - touch.x2) === 10 ) {
    deltaX = 10 + 9 + 8 + ... + 0;
}

4.2、处理tap,doubleTap,singleTap三者之间的关系

function cancelAll() {
  if (touchTimeout) clearTimeout(touchTimeout)
  if (tapTimeout) clearTimeout(tapTimeout)
  if (swipeTimeout) clearTimeout(swipeTimeout)
  if (longTapTimeout) clearTimeout(longTapTimeout)
  touchTimeout = tapTimeout = swipeTimeout = longTapTimeout = null
  // 这句很重要，将影响所有需要对touch对象属性判断的语句
  touch = {}
}
function endListener(e){
  tapTimeout = setTimeout(function() {
    var event = $.Event('tap')
    // tap事件对象event可以取消后续绑定的doubleTap, singleTap处理器
    event.cancelTouch = cancelAll
    touch.el.trigger(event)
    // 立即触发双击事件
    if (touch.isDoubleTap) {
      if (touch.el) touch.el.trigger('doubleTap')
      touch = {}
    }
    // 定时.25s后再触发单击事件
    else {
      touchTimeout = setTimeout(function() {
        touchTimeout = null
        if (touch.el) touch.el.trigger('singleTap')
        touch = {}
      }, 250)
    }
  }, 0)
}

例如：如何在tap事件处理器中取消 doubleTap或singleTap事件监听器

$('body')
  .on('tap', function(e){
    console.log('tap');
    // 执行下面语句将影响是否触发绑定的 doubleTap或singleTap 处理器
    e.cancelTouch();
  })
  .on('doubleTap', function(e){
    console.log('doubleTap');
  })
  .on('singleTap', function(e){
    console.log('singleTap');
  });
// 'tap'

5、兼容指针事件系统

// 判断是否是指针事件类型
function isPointerEventType(e, type) {
  return (e.type == 'pointer' + type ||
    e.type.toLowerCase() == 'mspointer' + type)
}
// 判断是否是第一个touch或pointer事件对象
function isPrimaryTouch(event) {
  return (event.pointerType == 'touch' ||
    event.pointerType == event.MSPOINTER_TYPE_TOUCH) && event.isPrimary
}
// 如果是指针类型是 pointerdown 或 pointermove 或 pointerup 且 不是第一个touch 或 pointer 事件对象，返回空，
// 直接屏蔽了第二个、第三...的触摸处理
if ((_isPointerType = isPointerEventType(e, 'down')) && !isPrimaryTouch(e)) return
if ((_isPointerType = isPointerEventType(e, 'move')) && !isPrimaryTouch(e)) return
if ((_isPointerType = isPointerEventType(e, 'up')) && !isPrimaryTouch(e)) return

6、 快捷注册事件

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

你可以用 on 方法注册事件，也可以快捷注册，下面两种方式都是一样的，类似jQuery用法

$('body').on('tap', function(){ console.log('body trigger tap event'); });
$('body').tap(function(){ console.log('body trigger tap event'); });

篇尾总结：

源码中大部分代码都已经解析完毕，如有不合理的地方，还请赐教，touch模块的中所有的事件都支持冒泡，但是不会对原生的touch事件产生影响，另外所有元素绑定的事件都是在文档document元素的touchend处理中触发，如果页面中有一元素在原生touch事件中阻止了冒泡，那么页面中所有元素注册的 zepto touch事件都不会被触发

转载于:https://my.oschina.net/colinfed/blog/534191