<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<style>
#box {
width: 400px;
height: 20px;
border: 1px solid #999;
margin: 0 auto;
text-align: center;
}
#box1 {
height: 100%;
width: 0px;
background-color: red;
}
</style>
</head>
<body>
<div id="box">
<div id="box1">
<span id="text"></span>
</div>
</div>
</body>
<script>
var i = 0
var a = function () {
if (i < 100) {
i++;
box1.style.width = i * 4 + 'px';
text.innerText = i + '%';
} else {
clearInterval(a);
text.innerText = '下载完成';
}
}
setInterval(a, 100);
</script>
</html>