Q:

Calling an external javascript from html

I have a javascript located on URL http://www.example.com/script.js.  When run, the script returns a UUID in the following format:
var uuid="AAAABBBBCCCCDDDD";

Every call to the JavaScript returns a random unique string. 
I have a simple HTML page with a single text box on it. 
I need to call the JavaScript before the page loads and put the above result into the textbox. 
I tried to use jQuery:
$.get(URL,callback); 

But that didn't work; No results were returned. 
How to I call an external JavaScript and put the result inside the textbox? 
EDIT: Here is the code I used:
<script language="javascript">
$(window).bind("load",start);

function start()
{
    alert("Inside");
    alert($.getScript("http://www.example.com/script.js")
}
</script>

I'm using this code inside a system that generated its own HTML code and I can't modify the <head> tag, so adding the JavaScript code there isn't an option. 
I tried using the above but it seems to break the code as no alert is shown.  If I remove the jQuery part, the "Inside" alert is shown. 
Do I need to reference jQuery in some way in order for it to work?  Is there another way to import JavaScript code without modifying the <head> tag? 

A:

Use $.getScript.  This will load and execute the script.  It has a callback that runs after the script is executed. 
function start() {
    $.getScript(URL, function() {
        $("#textbox").val(uuid);
    }
}

Displaying the return value of $.getScript is not useful.  It's an asynchronous function, it returns the jqXHR object that represents the AJAX call, not anything related to the script itself.  If you want to use what the script does, you have to do it in the callback.