Sometimes you have to load jQuery, but you don’t know if it has already been referenced somewhere else in the website.
This tends to happen if you have a custom web control, delivered in an assembly, that relies on jQuery.
This code has been ripped out of my application, and may have a typo or three, but it gives you the general idea.
var jQueryScriptOutputted = false;
function initJQuery() {
//if the jQuery object isn't available
if (typeof(jQuery) == 'undefined') {
if (! jQueryScriptOutputted) {
//only output the script once..
jQueryScriptOutputted = true;
//output the script (load it from google api)
document.write("<scr" + "ipt type=\"text/javascript\" src=\"http://ajax.googleapis.com/ajax/libs/jquery/1.3.2/jquery.min.js\"></scr" + "ipt>");
}
setTimeout("initJQuery()", 50);
} else {
$(function() {
//do anything that needs to be done on document.ready
});
}
}
initJQuery();