前端开发之tap点透浅谈(tap是什么意思)
一、点透是什么
你可能碰到过在列表页面上创建一个弹出层，弹出层有个关闭的按钮，你点了这个按钮关闭弹出层后后，这个按钮正下方的内容也会执行点击事件（或打开链接）。这个被定义为这是一个“点透”现象。
在前面的项目中遇到了如下图的问题：在点击弹出来的选择组件的右上角完成后会让完成后面的input输入框聚焦，弹出输入键盘，也就是点透了
二、为什么会出现点透？
我们来看看zepto源码里面看关于tap的实现方法：
;(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)复制代码
可以看出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，也就出现了上面的点透现象。
三、点透的解决方法：
方案一：引入fastclick
github链接：github.com/ftlabs/fast…
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
window.addEventListener( "load", function() {
FastClick.attach(document.body);
}, false );复制代码或者有zepto或者jqm的js里面加上
$(function() {
FastClick.attach(document.body);
});复制代码方案二：用touchend代替tap事件，并阻止touchend默认行为preventDefault()
$("#cbFinish").on("touchend", function (event) { // 很多处理比如隐藏什么的
event.preventDefault();
});复制代码方案三：延迟一定的时间(300ms+)来处理事件
$("#cbFinish").on("tap", function (event) {
setTimeout(function(){ //一些处理
},320);
});复制代码这种方法其实很好，可以和fadeInIn/fadeOut等动画结合使用，可以做出过渡效果。
作者：凌可语
链接：https://juejin.cn/post/7030288090262405156