A tip when running javascript dynamically 朱燚:

firefox works differently from ie when change src of a existing script , in ie this action cause the javascript engine to reload that script, and execute it ,while in firefox, nothing will happen

you can have your own test by following code

<script id="s1" type="text/javascript">
</script>
<script language="javascript" type="text/javascript">
document.getElementById("s1").src="1.js";

</script>

in 1.js we simply alert some message

alert("executed");

So if you want the browser to execute some js dynamically , you need to reload the script element.  Add a script element into DOM will cause the execution of the script in both browser ,following code shows how to reload a script element

if(this.element)

this.element.parentNode.removeChild(this.element);

this.element=document.createElement("SCRIPT");

this.element.type="text/javascript";

this.element.id = "MzJsonElement";

this.element.src=url;

document.getElementsByTagName("HEAD")[0].appendChild(this.element);

this might be helpful when  we need our browser to run some  json callback script