Javascript XMLResponse returning null

[aaronharwood]

I have read dozens of existing responses on threads, that span the last 5 years or so, concerning this problem and while there are many solutions that appear to work for others - none work for me.

I have some Javascript that is receiving an XML file from a Servlet. The problem is that the XMLResponse always returns a null value.

Here is some the code snippet:

...
function alertContents() {
   if (http_request.readyState == 4) {
      if (http_request.status == 200) {	 
    	 alert(http_request.readyState);
    	 alert(http_request.status);
    	 alert(http_request.getAllResponseHeaders()); 
    	 alert(http_request.responseText);
    	 alert(http_request.responseXML);
...

The alerts give the following outputs.

4

200

Date: Sat, 03 Jul 2010 08:44:44 GMT
Content-Length: 271
Server: Apache-Coyote/1.1
Content-Type: text/xml;charset=ISO-8859-1

<?xml version="1.0" encoding="UTF-8" standalone="no" ?><Console ConsoleType="Er rorConsole"><Co nsoleName>Serve r Error</ConsoleName><Er rorMessage>The Console servlet requires a consoleType parameter. This parameter was not found in the URL request.</ErrorMessage></Console>

null

As you can see, the content type iss text/xml. Pasting the XML into a validator gives a valid response. I really have no idea why the XMLResponse is returning null - there doesn't appear to be any reason to fail.

Using IE, the errorCode is 0, so there is no help there.

There does not appear to be any other way to debug this.

Any suggestions?

[acoder]

Check out the XMLHttpRequest responses in Firebug (Firefox Add-on).

[aaronharwood]

I found the problem - somewhere else in the script, before the request is made, there is a line that was forcing the mime type to be interpreted as text/html regardless of what the returned mime type was declared as. Removing that line fixed the problem.