如果尚未加载jquery，请加载它；如果没有可用的连接，请使用本地版本

Question

<script type="text/javascript">
if (typeof jQuery == 'undefined') {
var script = document.createElement('script');
script.type = "text/javascript";
script.src = "http://ajax.googleapis.com/ajax/libs/jquery/1.5.2/jquery.min.js";
document.getElementsByTagName('head')[0].appendChild(script);
}
</script>

Here is my current code. Is there any way to load a local copy of the jquery lib, if script.src = "http://ajax.googleapis.com/ajax/libs/jquery/1.5.2/jquery.min.js" fails? And is this script loaded asynchronous? Or will it freeze the ui thread until loaded?

Answer 1

You can just do this:

<script src="cdn.jquery.js"></script>
<script>window.jQuery || document.write('<script src="/local/jquery.js"><\/script>')</script>