Dynamic Loading of Javascript content

// from  http://ntt.cc/2008/02/10/4-ways-to-dynamically-load-external-javascriptwith-source.html
// TODO: will make mddn242 specific examples

	// you need to put an escape character before the closing </script> tag, like this: <\/script>

1. use document write
<script language="javascript">
document.write("<script src='other.js'><\/script>");
</script>

2. Dynamically change the src attribute
<script src='' id="s1"></script>
<script language="javascript">
s1.src="other.js"
</script>

3. Dynamically create a script element
<script>
var oHead = document.getElementsByTagName('HEAD').item(0);
var oScript= document.createElement("script");
oScript.type = "text/javascript";
oScript.src="other.js";
oHead.appendChild( oScript);
</script>

4.  Get JavaScript by using XMLHTTP,then create script object 
<script language="JavaScript">
function GetHttpRequest()
{
if ( window.XMLHttpRequest ) // Gecko
return new XMLHttpRequest() ;
else if ( window.ActiveXObject ) // IE
return new ActiveXObject("MsXml2.XmlHttp") ;
}
function AjaxPage(sId, url){
var oXmlHttp = GetHttpRequest() ;
oXmlHttp.OnReadyStateChange = function()
{
if ( oXmlHttp.readyState == 4 )
{
if ( oXmlHttp.status == 200 || oXmlHttp.status == 304 )
{
IncludeJS( sId, url, oXmlHttp.responseText );
}
else
{
alert( 'XML request error: ' + oXmlHttp.statusText + ' (' + oXmlHttp.status + ')' ) ;
}
}
}
oXmlHttp.open('GET', url, true);
oXmlHttp.send(null);
}
function IncludeJS(sId, fileUrl, source)
{
if ( ( source != null ) && ( !document.getElementById( sId ) ) ){
var oHead = document.getElementsByTagName('HEAD').item(0);
var oScript = document.createElement( "script" );
oScript.language = "javascript";
oScript.type = "text/javascript";
oScript.id = sId;
oScript.defer = true;
oScript.text = source;
oHead.appendChild( oScript );
}
}
AjaxPage( "scrA", "b.js" );
alert( "dynamically load javascript");
alert( "dynamically load a.js and get the variable：" + str );
</script>