encounter problem while uploading file using jquery.form plugin

encounter problem while uploading file using jquery.form plugin

I'm using jQuery.form to upload a file to the remote server, and I know jQuery.form implement this by embedding an invisible iframe. Since the dataType I set is 'script', i need to wrap the returned Javascript with <textarea> to let the plugin execute the Javascript properly, but after I do all of the above, it doesn't work, the Javascript never get executed.