Auto include javascript file if not already included

Answer 1

http://www.cryer.co.uk/resources/javascript/script17_include_js_from_js.htm

Answer 2

You can do something like this:

$(function() {
    if($('#yourscriptid').length == 0) {
        document.getElementsByTagName('head').item(0).innerHTML+='<script id="yourscriptid" type="text/javascript" src="path/to/script"></script>';
    }
});

Answer 3

Well if that JavaScript file defines a specific variable (or a function) you can check its presence by checking typeof that_variable, then load the JavaScript file if necessary. An example, here is how you load swfobject library if its not available on the page:

if (typeof swfobject == "undefined") {
   var e = document.createElement("script");
   e.src = "http://ajax.googleapis.com/ajax/libs/swfobject/2/swfobject.js";
   e.type = "text/javascript";
   document.getElementsByTagName("head")[0].appendChild(e); 
}