XMLHttpRequest to get HTTP response from remote host

Question

Why the following code Based on Mozilla example does not work? Tried with Firefox 3.5.7 & Chrome.

Answer 1

Your browser is preventing cross-site scripting. You have to use a relative path, otherwise most browsers will simply return an error or an empty responseText.

The following Stack Overflow post is probably also related to your problem:

• Empty responseText from XMLHttpRequest.

Answer 2

Security issue no?

Presumably firefox is preventing the local file from talking to a remote host?

Scouting round the net - found this. Try adding this to the start of your script:

try {
  netscape.security.PrivilegeManager.enablePrivilege("UniversalBrowserRead");
} catch (e) {
  alert("Permission UniversalBrowserRead denied.");
}

Can't guarantee this'll work; because ultimately what you're trying to do is enter a security hole that browsers have been specifically coded to have plugged up (cross-domain requests).

There are some special scenarios where it can be switched on, though, usually at the user's discretion.

Answer 3

I'm also assuming that you've opened your HTML test page directly in the browser judging by your reference to file:///.... For XMLHttpRequest calls, you need to serve the HTML from a server. Try something like xampp (http://www.apachefriends.org/en/xampp.html) to get a local server up and running and then run your test from http://localhost/XMLHTTP.html.

Note, this does not solve your same-origin problem, but this would allow the following code to work:

  <script>
    var req = new XMLHttpRequest();
    req.open('GET', '/myTestResponse.html', false); 
    req.send();
    if(req.status == 200) {
        alert(req.responseText);
    }
  </script>

Answer 4

You cannot make requests across domains, even with local files.

https://developer.mozilla.org/en/Same_origin_policy_for_JavaScript

Unless you are developing an extension, which does not have the same restrictions as a web page.