<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>Document</title>
<style>
* {
margin: 0;
padding: 0;
}
.box {
width: 200px;
height: 200px;
background: #ff0;
}
</style>
</head>
<body>
<div class="box"></div>
<br /><br />
<button id="btn1">放大</button>
<br />
<br />
<button id="btn2">缩小</button>
<script>
var box = document.querySelector(".box");
var btn1 = document.getElementById("btn1");
var btn2 = document.getElementById("btn2");
btn1.onclick = function () {
var timer = setInterval(function () {
box.style.width = box.offsetWidth + 5 + "px";
if (box.offsetWidth >= 400) {
clearInterval(timer);
}
}, 100);
};
btn2.onclick = function () {
var timer = setInterval(function(){
box.style.width = box.offsetWidth - 5 + "px";
if(box.offsetWidth <= 200) {
clearInterval(timer);
}
},100)
}
</script>
</body>
</html>