場景描述
在使用JS控制動畫時一般需要在動畫結束后執行回調去進行DOM的相關操作，所以需要監聽動畫結束進行回調。JS提供了以下事件用於監聽動畫的結束，簡單總結學習下。
CSS3動畫監聽事件
transitionEnd事件
transitionEnd事件會在CSS transition動畫結束后觸發。
動畫結束后觸發監聽事件
<!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">
鼠標移入
</div>
<script type="text/javascript">
var element = document.getElementById('demo')
element.addEventListener('transitionend', handle, false)
function handle(){
alert('transitionend事件觸發')
}
</script>
</body>
</html>
事件多次觸發問題
當存在多個屬性過渡變化時，結束時會多次觸發transitionend事件。看個例子：
當過渡結束時，width和background-color都發生變化，會觸發兩次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事件觸發')
}
function change() {
element.className = element.className === 'demo' ? 'demo w200': 'demo'
}
</script>
</body>
</html>
事件失效問題及解決方案
1、在transiton動畫完成前設置display:none，事件不會觸發。
<!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事件觸發')
}
function change() {
element.className = element.className === 'demo' ? 'demo w200': 'demo'
// 500ms后設置display:none
setTimeout(function (){
element.style.display = 'none'
},400)
}
</script>
</body>
</html>
2、當transition完成前移除transition一些屬性時，事件也不會觸發，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事件觸發')
}
function change() {
element.className = element.className === 'demo' ? 'demo w200': 'demo'
setTimeout(function(){
element.className = 'noTranstion'
},400)
}
</script>
</body>
</html>
3、元素從display:none到block，不會有過渡，導致無法觸發transitionend事件
例如：元素從display:none 到block opacity從0到1，無法觸發過渡效果。
<!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事件觸發')
}
function change() {
element.className = element.className === 'demo' ? 'demo opt': 'demo'
}
</script>
</body>
</html>
無法觸發過渡效果原因：
元素從none到block，剛生成未能即時渲染，導致過渡失效。所以需要主動觸發頁面重繪，刷新DOM。頁面重繪可以通過改變一些CSS屬性來觸發，例如：offsetTop、offsetLeft、offsetWidth、scrollTop等。
觸發過渡效果解決方案：
1、通過定時器延遲渲染
<!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()">點擊</button>
<script type="text/javascript">
var element = document.getElementById('demo')
var button = document.getElementById('button')
element.addEventListener('transitionend', handle, false)
function handle(){
alert('transitionend事件觸發')
}
function change() {
element.className = element.className === 'demo' ? 'demo opt': 'demo'
if(element.className === 'demo'){
element.style.opacity = null
button.innerHTML = '點擊'
}else{
setTimeout(function(){
element.style.opacity = '1'
button.innerHTML = '重置'
},10)
}
}
</script>
</body>
</html>
2、強制獲取當前內聯樣式
通過window.getComputedStyle()方法返回應用樣式后的元的所有CSS屬性的值，並解析這些值可能包含的任何基本計算。也就是說返回的屬性值是已計算后的值，即DOM元素的樣式已經更新了。然后再改變對應屬性值觸發過渡效果。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()">點擊</button>
<script type="text/javascript">
var element = document.getElementById('demo')
var button = document.getElementById('button')
element.addEventListener('transitionend', handle, false)
function handle(){
alert('transitionend事件觸發')
}
function change() {
element.className = element.className === 'demo' ? 'demo opt': 'demo'
if(element.className === 'demo'){
element.style.opacity = null
button.innerHTML = '點擊'
}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、觸發重繪刷新DOM
通過clientWidth觸發重繪，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()">點擊</button>
<script type="text/javascript">
var element = document.getElementById('demo')
var button = document.getElementById('button')
element.addEventListener('transitionend', handle, false)
function handle(){
alert('transitionend事件觸發')
}
function change() {
element.className = element.className === 'demo' ? 'demo opt': 'demo'
if(element.className === 'demo'){
element.style.opacity = null
button.innerHTML = '點擊'
}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>
瀏覽器兼容性
移動端基本支持 android2.1+、webkit3.2+
詳見瀏覽器兼容性
animationEnd事件
與transitonend事件類似，詳見
Zepto中animate結束回調實現
查看了下zepto動畫模塊的源代碼，animate()方法在動畫結束后觸發回調也是通過transitionend、animationend事件來觸發。
另外在一些低版本的Android手機可能無法觸發transitionend事件，需要手動觸發。
$.fx = {
off: (eventPrefix === undefined && testEl.style.transitionProperty === undefined),
speeds: { _default: 400, fast: 200, slow: 600 },
cssPrefix: prefix,
transitionEnd: normalizeEvent('TransitionEnd'),
animationEnd: normalizeEvent('AnimationEnd')
}
// 手動觸發事件
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)
}
參考鏈接
zepto動畫模塊源碼
transitionend事件MDN
transtion屬性詳解MDN
transitionend事件詳解
Window.getComputedStyle() 方法