Using javascript to check which CDN jQuery is cached from on the client

Question

Can I use JavaScript to check whether JQuery is (already) downloaded (cached) on the target web browser (user) or not? For Example:

If (JQuery-from-Microsoft-CDN-downloaded)
    Then use http://ajax.aspnetcdn.com/ajax/jQuery/jquery-1.4.4.js
Else if (JQuery-from-Google-APIs- downloaded)
    Then use http://ajax.googleapis.com/ajax/libs/jquery/1.3.2/jquery.min.js
Else if (JQuery-from-code.jquery.com- downloaded)
    Then use http://code.jquery.com/jquery-1.4.4.min.js
Else use jQuery from my own website.

Means that using the ability of javascript to check whether one of them is downloaded on the target User (Web Browser), if not then use jQuery from my own website otherwise if true then use that version of JQuery that is downloaded on the target User.

Answer 1

You can't do this, another case where the same-origin policy prevents any mechanism to accomplish this. If you think about it, it makes sense...any mechanism you could use to accomplish this, you could also use to figure out which sites someone visited, by seeing which files they have cached.