requestAnimationFrame的作用就是重绘
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
<style>
#box{
background-color: rebeccapurple;
width: 100px;
height: 100px;
}
</style>
</head>
<body>
<div id="box"></div>
<script>
var duration = 4000.0;
var startTime = -1.0;
function render(currentTime) {
var h1 = document.getElementById("box");
var opacity = currentTime/duration;
h1.style.opacity = opacity;
}
function eachFrame() {
var timeElapse = (new Date()).getTime()-startTime;
if(startTime < 0) {
startTime = (new Date()).getTime();
render(0.0);
}else if(timeElapse < duration) {
render(timeElapse);
}else {
return;
}
window.requestAnimationFrame(eachFrame);
}
window.requestAnimationFrame(eachFrame);
</script>
</body>
</html>原文：https://www.cnblogs.com/ye-hcj/p/10352988.html