Why does jQuery load twice in my GreaseMonkey Script

Question

for some reason my Firefox4+GreaseMonkey Script loads jQuery twice. I copy'n'pasted the following snippet, the "test" alert shows twice.

Regards

var $;
// Add jQuery
(function(){
 if (typeof unsafeWindow.jQuery == 'undefined') {
 var GM_Head = document.getElementsByTagName('head')[0] || document.documentElement,
 GM_JQ = document.createElement('script');
 GM_JQ.src = 'http://ajax.googleapis.com/ajax/libs/jquery/1/jquery.min.js';
 GM_JQ.type = 'text/javascript';
 GM_JQ.async = true;
 GM_Head.insertBefore(GM_JQ, GM_Head.firstChild);
 }
 GM_wait();
})();
// Check if jQuery's loaded
function GM_wait() {
 if (typeof unsafeWindow.jQuery == 'undefined') {
 window.setTimeout(GM_wait, 100);
 } else {
 $ = unsafeWindow.jQuery.noConflict(true);
 letsJQuery();
 }
}
// All your GM code must be inside this function
function letsJQuery() {
 alert("test");
}

Answer 1

This is probably because the target page is loading frames or iframes.

Add these lines to the top of the code-portion of your script:

if (window.top != window.self) //-- Don't run on frames or iframes
 return;

Also, if you are just using FF + GM, don't bother with all that rigamarole to load jQuery. GM now works with the later jQuery versions.

Just add a line like:

// @require http://ajax.googleapis.com/ajax/libs/jquery/1.5.1/jquery.min.js

into your script's metadata block. jQuery will be copied once onto your local machine and run from there -- eliminating what can sometimes be a few seconds delay in your script's runtime.

And such scripts can run in Chrome, if you use one of the GM-emulating extensions like TamperMonkey.

• Fabian Zeindl: Great. Thanks a million times!
• Rick: God I would never get the answer without your answer.