动态加载js的几种方法

1.直接document.write
<script language=javascript>
document.write（<script src="test.js"></script>）;
</script>
2.动态改变已有script的src属性
<script src="" id=s1></script>
<script language=javascript>
s1.src=test.js
</script>
3.动态创建script元素
<script>
var s2 = document.createElement（script）;
s2.src=test.js
document.body.insertAdjacentElement（BeforeBegin,s2）;
</script>
<head>
<script>
function loadJs（file）{
var scriptTag = document.getElementById（"loadScript"）;
var head = document.getElementsByTagName（"head"）.item（0）
if（scriptTag） head.removeChild（scriptTag）;
script = document.createElement（"script"）;
script.src = file;
script.type = "text/javascript";
script.id = "loadScript";
head.appendChild（script）
}
</script>
</head>
<body onload=loadJs（"1.js"）;loadJs（"2.js"）>