Loading jQuery multiple times in the same page

I'm implementing a plug-in that's embeddable in different sites (a la Meebo, Wibiya), and I want to use jQuery. Problem is, the site I'm embedding to, may already have a jQuery script loaded.

The question is, what's the best approach for this kind of problem:

1. Should I just check if jQuery is already loaded and if so, use the original site's jQuery, otherwise load it myself? If I use this approach, am I not risking comaptibility problems (i.e. the site uses an old version of jQuery)?

2. Should I load jQuery myself (whether it's already loaded or not) and call "jQuery.noConflict(true)" when it's finis开发者_如何学JAVAhed loading? If so, how can I make sure that my jQuery has finished loading (hooking to the onLoad event doesn't seem to work all the time, and polling for "jQuery" won't work for obvious reasons)?

3. Should I do something else?

Thanks.

You can check if jQuery is already loaded using the code:

if(jQuery) {
     //it's loaded
} else {
     //it's not loaded
}

You can also check the version of the loaded jQuery using:

$().jquery;

this will return a string like "1.4.1"

Using these two methods you can see what the site has already loaded and act accordingly.

By this blog article

if (typeof jQuery == 'undefined') {  
    // jQuery is not loaded  
} else {
    // jQuery is loaded
}