基本原理是父容器的高度设置为0，超出部分overflow:hidden，在事件触发或者方法被调用的时候更改父元素的高度即可.动态的改变父元素的高度就可以实现对应的效果，可以加入缓动动画公式来实现。
<!DOCTYPE html>
<html>
<head>
<title></title>
<style type="text/css">
#box{
height: 0;
overflow: hidden;
}
#div{
background: blue;width: 100px;min-height: 200px;
}
</style>
</head>
<body>
<span id="span">展开</span>
<div id="box">
<div style="" id="div">我是div
我是div<br/>
</div>
</div>
<script type="text/javascript">
var tween = {
linear: function (t,b,c,d) {
return c*t/d +b;
},
easeIn: function () {
return c* (t/=d)*t +b;
}
}
var Animate = function (dom) {
this.dom = dom; // 进行运动的dom节点
this.startTime = 0; // 动画开始的时间
this.startPos = 0; // 动画开始时dom节点的位置
this.endPos = 0;
this.propertyName = null;
this.easing = null;
this.duration = null;
}
Animate.prototype.start = function (propertyName,endPos,duration,easing,fn) {
this.startTime = +new Date;
this.startPos = this.dom.getBoundingClientRect()[propertyName]
this.propertyName = propertyName
this.endPos = endPos;
this.duration = duration
this.easing = tween[easing]
var self = this;
var timeId = setInterval(function () {
if (self.step() === false) {
clearInterval(timeId)
fn && fn()
}
}, 19)
}
Animate.prototype.step = function () {
var t = +new Date;
if (t>=this.startTime + this.duration){
this.update(this.endPos)
return false
}
var pos = this.easing(t -this.startTime,this.startPos,this.endPos - this.startPos,this.duration)
this.update(pos)
}
Animate.prototype.update = function (pos) {
this.dom.style[this.propertyName] = pos + 'px'
}
var div = document.getElementById('div')
var box = document.getElementById('box')
let sty = '收起'
let initPos = 0;
// alert(div.offsetHeight)
document.getElementById('span').onclick = function () {
let realH = div.offsetHeight
var animate = new Animate(box);
if (initPos !== 0) {
animate.start('height', 0, 1000, 'linear',function(){
initPos = 0
})
return;
}
console.log(realH, div.style.height)
animate.start('height', realH, 1000, 'linear',function(){
initPos = box.offsetHeight
})
}
</script>
</body>
</html>
