<script src="a.js"><//script>
<script src="b.js"><//script>

document.write('<script src="a.js"><//script>')
document.write('<script src="b.js"><//script>')

function include(path){
var a=document.createElement("script");
a.type = "text/javascript";
a.src=path;
var head=document.getElementsByTagName("head")[0];
head.appendChild(a);
}

include("a.js")

include("b.js")