abstract：<!DOCTYPE html><html lang="en"><head> <meta charset="UTF-8"> <title>changeDiv</title> <style type=&quo
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>changeDiv</title>
<style type="text/css">
#box{width: 100px;height:100px;background:red;margin: 20px 80px;}
</style>
</head>
<body>
<!--用按钮控制DIV的高度、宽度、颜色、重置、隐藏、显示-->
<div id="box"></div>
<input type="button" value="变高" onclick="aa()">
<input type="button" value="变宽" onclick="bb()">
<input type="button" value="变色" onclick="cc()">
<input type="button" value="重置" onclick="dd()">
<input type="button" value="隐藏" onclick="ee()">
<input type="button" value="显示" onclick="ff()">
<script type="text/javascript">
var box;
window.onload=function(){
box=document.getElementById('box');
}
//改变高度
function aa(){
box.style.height="400px";
}
//改变宽度
function bb(){
box.style.width="400px";
}
function cc(){
box.style.background="pink";
}
function dd(){
box.style.height="100px";
box.style.width="100px";
box.style.background="red";
}
function ee(){
box.style.display="none";
}
function ff(){
box.style.display="block";
}
</script>
</body>
</html>
总结：var box;
window.onload=function(){
box=document.getElementById('box');
}是相当于window.box=document.getElementById('box')吗？
Correcting teacher：灭绝师太Correction time：2018-10-29 18:05:24
Teacher's summary：不能划等号，直接写window.box，那么加载js的时候如果没有 id="box"的元素, window.box就等于undefined
