title: javascript cross-domain request iframe VS jsonp
body: <p>I am writing an app that my client uses given javascript, which will collect some HTML data and post to my server.  No data will be returned from my server.  </p>
  
  <p>Iframe and Jsonp are two options. I wonder what's the pro and con of each given my situation. Is there any security hole involved in one of them?</p>
  
  <p>another question is how can i identify the user?  say one person copied the javascript and put on his website. </p>