Zepto.js touch模块深入分析

目的：记录 Zepto.js touch模块 源码阅读

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，慎重慎重...，至此完毕，感谢阅读！！