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')