JS如何监听动画结束
场景描述
在使用JS控制动画时一般需要在动画结束后执行回调去进行DOM的相关操作，所以需要监听动画结束进行回调。JS提供了以下事件用于监听动画的结束，简单总结学习下。
CSS3动画监听事件
transitionEnd事件
transitionEnd事件会在CSS transition动画结束后触发。
动画结束后触发监听事件
<!DOCTYPE html>
<html>
<head>
<title>transtionend demo</title>
<style type="text/css">
*{margin:0;padding: 0;}
.demo{
margin:100px;
width:100px;
height: 100px;
background-color: #ddc;
transition: all 0.5s ease-out;
}
.demo:hover{
width: 200px;
}
</style>
</head>
<body>
<div id="demo" class="demo">
鼠标移入
</div>
<script type="text/javascript">
var element = document.getElementById('demo')
element.addEventListener('transitionend', handle, false)
function handle(){
alert('transitionend事件触发')
}
</script>
</body>
</html>
事件多次触发问题
当存在多个属性过渡变化时，结束时会多次触发transitionend事件。看个例子：
当过渡结束时，width和background-color都发生变化，会触发两次transionend事件
<!DOCTYPE html>
<html>
<head>
<title>transtionend demo</title>
<style type="text/css">
*{margin:0;padding: 0;}
.demo{
width:100px;
height: 100px;
background-color: #ddc;
transition: all 0.5s ease-out;
}
.w200{
width: 200px;
background-color: #fef;
}
</style>
</head>
<body>
<div id="demo" class="demo" onmouseover="change()" onmouseout="change()">
</div>
<script type="text/javascript">
var element = document.getElementById('demo')
element.addEventListener('transitionend', handle, false)
function handle(){
alert('transitionend事件触发')
}
function change() {
element.className = element.className === 'demo' ? 'demo w200': 'demo'
}
</script>
</body>
</html>
事件失效问题及解决方案
1、在transiton动画完成前设置display:none，事件不会触发。
<!DOCTYPE html>
<html>
<head>
<title>transtionend demo</title>
<style type="text/css">
*{margin:0;padding: 0;}
.demo{
width:100px;
height: 100px;
background-color: #ddc;
transition: all 0.5s ease-out;
}
.w200{
width: 200px;
}
</style>
</head>
<body>
<div id="demo" class="demo" onmouseover="change()" onmouseout="change()">
</div>
<script type="text/javascript">
var element = document.getElementById('demo')
element.addEventListener('transitionend', handle, false)
function handle(){
alert('transitionend事件触发')
}
function change() {
element.className = element.className === 'demo' ? 'demo w200': 'demo'
// 500ms后设置display:none
setTimeout(function (){
element.style.display = 'none'
},400)
}
</script>
</body>
</html>
2、当transition完成前移除transition一些属性时，事件也不会触发，例如：
<!DOCTYPE html>
<html>
<head>
<title>transtionend demo</title>
<style type="text/css">
*{margin:0;padding: 0;}
.demo{
width:100px;
height: 100px;
background-color: #ddc;
transition: all 0.5s ease-out;
}
.noTranstion{
width:100px;
height: 100px;
background-color: #ddc;
}
.w200{
width: 200px;
}
</style>
</head>
<body>
<div id="demo" class="demo" onmouseover="change()" onmouseout="change()">
</div>
<script type="text/javascript">
var element = document.getElementById('demo')
element.addEventListener('transitionend', handle, false)
function handle(){
alert('transitionend事件触发')
}
function change() {
element.className = element.className === 'demo' ? 'demo w200': 'demo'
setTimeout(function(){
element.className = 'noTranstion'
},400)
}
</script>
</body>
</html>
3、元素从display:none到block，不会有过渡，导致无法触发transitionend事件
例如：元素从display:none 到block opacity从0到1，无法触发过渡效果。
<!DOCTYPE html>
<html>
<head>
<title>transtionend demo</title>
<style type="text/css">
*{margin:0;padding: 0;}
body{padding: 50px;}
.demo{
width:100px;
height: 100px;
background-color: #ddc;
transition: all 0.5s ease-out;
opacity:0;
display: none;
}
.noTranstion{
width:100px;
height: 100px;
background-color: #ddc;
}
.opt{
display: block;
opacity:1
}
.w200{
width: 200px;
}
button{position: absolute;top: 200px;width: 100px;height: 40px;}
</style>
</head>
<body>
<div id="demo" class="demo" onmouseover="change()" onmouseout="change()">
</div>
<button onclick="change()">Click</button>
<script type="text/javascript">
var element = document.getElementById('demo')
element.addEventListener('transitionend', handle, false)
function handle(){
alert('transitionend事件触发')
}
function change() {
element.className = element.className === 'demo' ? 'demo opt': 'demo'
}
</script>
</body>
</html>
无法触发过渡效果原因：
元素从none到block，刚生成未能即时渲染，导致过渡失效。所以需要主动触发页面重绘，刷新DOM。页面重绘可以通过改变一些CSS属性来触发，例如：offsetTop、offsetLeft、offsetWidth、scrollTop等。
触发过渡效果解决方案：
1、通过定时器延迟渲染
<!DOCTYPE html>
<html>
<head>
<title>transtionend demo</title>
<style type="text/css">
*{margin:0;padding: 0;}
body{padding: 50px;}
.demo{
width:100px;
height: 100px;
background-color: #ddc;
transition: all 0.5s ease-out;
opacity: 0;
display: none;
}
.opt{
display: block;
}
button{position: absolute;top: 200px;width: 100px;height: 40px;}
</style>
</head>
<body>
<div id="demo" class="demo">
</div>
<button id="button" onclick="change()">点击</button>
<script type="text/javascript">
var element = document.getElementById('demo')
var button = document.getElementById('button')
element.addEventListener('transitionend', handle, false)
function handle(){
alert('transitionend事件触发')
}
function change() {
element.className = element.className === 'demo' ? 'demo opt': 'demo'
if(element.className === 'demo'){
element.style.opacity = null
button.innerHTML = '点击'
}else{
setTimeout(function(){
element.style.opacity = '1'
button.innerHTML = '重置'
},10)
}
}
</script>
</body>
</html>
2、强制获取当前内联样式
通过window.getComputedStyle()方法返回应用样式后的元的所有CSS属性的值，并解析这些值可能包含的任何基本计算。也就是说返回的属性值是已计算后的值，即DOM元素的样式已经更新了。然后再改变对应属性值触发过渡效果。例如：
<!DOCTYPE html>
<html>
<head>
<title>transtionend demo</title>
<style type="text/css">
*{margin:0;padding: 0;}
body{padding: 50px;}
.demo{
width:100px;
height: 100px;
background-color: #ddc;
transition: all 0.5s ease-out;
opacity: 0;
display: none;
}
.opt{
display: block;
}
button{position: absolute;top: 200px;width: 100px;height: 40px;}
</style>
</head>
<body>
<div id="demo" class="demo">
</div>
<button id="button" onclick="change()">点击</button>
<script type="text/javascript">
var element = document.getElementById('demo')
var button = document.getElementById('button')
element.addEventListener('transitionend', handle, false)
function handle(){
alert('transitionend事件触发')
}
function change() {
element.className = element.className === 'demo' ? 'demo opt': 'demo'
if(element.className === 'demo'){
element.style.opacity = null
button.innerHTML = '点击'
}else{
// setTimeout(function(){
// element.style.opacity = '1'
// button.innerHTML = '重置'
// },10)
window.getComputedStyle(element, null).opacity
element.style.opacity = '1'
button.innerHTML = '重置'
}
}
</script>
</body>
</html>
3、触发重绘刷新DOM
通过clientWidth触发重绘，例如：
<!DOCTYPE html>
<html>
<head>
<title>transtionend demo</title>
<style type="text/css">
*{margin:0;padding: 0;}
body{padding: 50px;}
.demo{
width:100px;
height: 100px;
background-color: #ddc;
transition: all 0.5s ease-out;
opacity: 0;
display: none;
}
.opt{
display: block;
}
button{position: absolute;top: 200px;width: 100px;height: 40px;}
</style>
</head>
<body>
<div id="demo" class="demo">
</div>
<button id="button" onclick="change()">点击</button>
<script type="text/javascript">
var element = document.getElementById('demo')
var button = document.getElementById('button')
element.addEventListener('transitionend', handle, false)
function handle(){
alert('transitionend事件触发')
}
function change() {
element.className = element.className === 'demo' ? 'demo opt': 'demo'
if(element.className === 'demo'){
element.style.opacity = null
button.innerHTML = '点击'
}else{
// setTimeout(function(){
// element.style.opacity = '1'
// button.innerHTML = '重置'
// },10)
// window.getComputedStyle(element, null).opacity
element.clientWidth;
element.style.opacity = '1'
button.innerHTML = '重置'
}
}
</script>
</body>
</html>
浏览器兼容性
移动端基本支持 android2.1+、webkit3.2+
详见浏览器兼容性
animationEnd事件
与transitonend事件类似，详见
Zepto中animate结束回调实现
查看了下zepto动画模块的源代码，animate()方法在动画结束后触发回调也是通过transitionend、animationend事件来触发。
另外在一些低版本的Android手机可能无法触发transitionend事件，需要手动触发。
$.fx = {
off: (eventPrefix === undefined && testEl.style.transitionProperty === undefined),
speeds: { _default: 400, fast: 200, slow: 600 },
cssPrefix: prefix,
transitionEnd: normalizeEvent('TransitionEnd'),
animationEnd: normalizeEvent('AnimationEnd')
}
// 手动触发事件
if (duration > 0){
this.bind(endEvent, wrappedCallback)
// transitionEnd is not always firing on older Android phones
// so make sure it gets fired
setTimeout(function(){
if (fired) return
wrappedCallback.call(that)
}, ((duration + delay) * 1000) + 25)
}
参考链接
zepto动画模块源码
transitionend事件MDN
transtion属性详解MDN
transitionend事件详解
Window.getComputedStyle() 方法
