XMLHttpRequest status 0 (responseText is empty)

Question

Cannot get data with XMLHttpRequest (status 0 and responseText is empty):

 xmlhttp=new XMLHttpRequest(); xmlhttp.open("GET","http://www.w3schools.com/XML/cd_catalog.xml", true); xmlhttp.onreadystatechange=function()  {   if(xmlhttp.readyState==4)     alert("status " + xmlhttp.status); } xmlhttp.send(); 

It alerts "status 0".

The same situation with the localhost request (cd_catalog.xml is saved as a local file)

 xmlhttp.open("GET","http://localhost/cd_catalog.xml", true); 

But with the localhost IP request

 xmlhttp.open("GET","http://127.0.0.1/cd_catalog.xml", true); 

and with the local file request

 xmlhttp.open("GET","cd_catalog.xml", true); 

everything is OK (status 200)

What can cause the problem (status=0) with the online request?

PS: Live HTTP Headers shows that everything is OK in all 4 cases:

   HTTP/1.1 200 OK   Content-Length: 4742 

PS2: Apache local web server on VMWare (host OS Win7, Guest OS Ubuntu, Network adapter – NAT). Browser – Firefox.

Answer 1

status is 0 when your html file containing the script is opened in the browser via the file scheme. Make sure to place the files in your server (apache or tomcat whatever) and then open it via http protocol in the browser. (i.e. http://localhost/myfile.html) This is the solution.

Answer 2

The cause of your problems is that you are trying to do a cross-domain call and it fails.

If you're doing localhost development you can make cross-domain calls - I do it all the time.

For Firefox, you have to enable it in your config settings

signed.applets.codebase_principal_support = true 

Then add something like this to your XHR open code:

  if (isLocalHost()){     if (typeof(netscape) != 'undefined' && typeof(netscape.security) != 'undefined'){       netscape.security.PrivilegeManager.enablePrivilege('UniversalBrowserRead');     }   } 

For IE, if I remember right, all you have to do is enable the browser's Security setting under "Miscellaneous → Access data sources across domains" to get it to work with ActiveX XHRs.

IE8 and above also added cross-domain capabilities to the native XmlHttpRequest objects, but I haven't played with those yet.