时间：2021-07-01 10:21:17 帮助过：38人阅读
<!DOCTYPE html><html>
<head>
<meta charset="UTF-8">
<title></title>
<style type="text/css">
p{
width: 100px;
height: 100px;
background: red;
margin-left: 50px;
margin-top: 30px;
display: none;
}
</style>
<script type="text/javascript">//
window.onload=function(){//
function btn(obj){//
var box=document.getElementById(obj);//
box.style.display="block";//
}//
}
function btn(obj){
var box=document.getElementById(obj);
box.style.display="block";
} </script>
</head>
<body>
<button onclick="btn('box1')" >显示第一个盒子</button>
<button onclick="btn('box2')">显示第二个盒子</button>
<button onclick="btn('box3')" >显示第三个盒子</button>
<button onclick="btn('box4')">显示第四个盒子</button>
<p id="box1">1</p>
<p id="box2">2</p>
<p id="box3">3</p>
<p id="box4">4</p>
</body></html>这种情况下，如果把js放在window.onload里面会报错。 
解析：放在onload中的js会等html加载完再执行函数，但是在加载html的时候，里面有onclick="btn('box1')"，会找不到这个函数（由于这个时候函数还没有加载）。要调用这个函数，就要让它加载完毕。
<!DOCTYPE html><html><head> <meta charset="UTF-8"> <title>111</title> <style> * {
margin: 0;
padding: 0;
list-style-type: none;
}
#box {
width: 360px;
padding-top: 360px;
background:url(image/01big.jpg) no-repeat center top;
margin: 100px auto;
border: 1px solid blueviolet;
overflow: hidden;
}
ul {
border-top: 1px solid blueviolet;
}
li {
float: left;
}
</style> <script> window.onload=function() {
var box =document.getElementById("box");
function fun(id,bg) {
var ID =document.getElementById(id);
ID.onmouseover=function() {
box.style.backgroundImage=bg;
}
} fun("id1","url(image/01big.jpg)");
fun("id2","url(image/02big.jpg)");
fun("id3","url(image/03big.jpg)");
fun("id4","url(image/04big.jpg)");
fun("id5","url(image/05big.jpg)");
}
<script>
window.onload=function(){
var box =document.getElementById("box"); function fun(id,bg){
var ID =document.getElementById(id);
ID.onmouseover=function(){
box.style.backgroundImage=bg;
}
}
fun("id1","url(image/01big.jpg)");
fun("id2","url(image/02big.jpg)");
fun("id3","url(image/03big.jpg)");
fun("id4","url(image/04big.jpg)");
fun("id5","url(image/05big.jpg)");
} </script></head><body>
<p id="box">
<ul>
<li id="id1"><img src="image/01.jpg" alt=""/></li>
<li id="id2"><img src="image/02.jpg" alt=""/></li>
<li id="id3"><img src="image/03.jpg" alt=""/></li>
<li id="id4"><img src="image/04.jpg" alt=""/></li>
<li id="id5"><img src="image/05.jpg" alt=""/></li>
</ul>
</p></body></html>以上就是window.onload的使用方法的详细内容，更多请关注Gxl网其它相关文章！