NS_ERROR_FAILURE with JS XMLHttpRequest

Question

I'm trying to load the source of a web page, as shown in "Javascript:The Definitive Guide" p.481, using firefox.

Here's my code:

  var request = new XMLHttpRequest();

  request.open("GET", "http://finance.yahoo.com/q?s=PG", false);

  request.send(null);

  if (request.status==200)  { alert(request.responseText);  }

  else {alert("Error "+request.status + ": "+request.statusText);} 

  </script>  

Firebug shows the GET statement, followed by 200 OK X 338ms.

Which looks like it was successful (code 200).

But the next Firebug line says: NS_ERROR_FAILURE, request.send(null);, with no further explanation.

and neither alert gets executed.

It doesn't help if I use help mode, and doesn't run in Chrome either. I don't have a popup or cookie or ad blocker running.

The page loads fine in perl with an LWP get().

If this is an inevitable cross-domain taboo, why doesn't the "definitive guide" say so?

I understand that JSONP returns JSON. I don't want that - I want just a string with the raw source, like with the perl LWP get().

Is this impossible with Javascript?

I suppose I could write a batch file which uses perl to get the source and put it into a JSON file whose name is hard-coded into the JS. But I'd like to avoid that sort of kludge.

Answer 1

In case it helps, I have run into this problem a couple times before, and ran into it again. If the answer to this question doesn't help you, try adding the following lines which helped me:

request.overrideMimeType('text/xml; charset=UTF-8'); // needed to get utf8 req's to work

or this debug line (which you can monitor on the web console of your browser)

request.onreadystatechange = function() {console.log("statechanged. url= " + url);};

before your

request.open()

where url is a var that holds the url you are trying to request. Sometimes it will give you that cryptic error if there is a problem getting the url, in my (last) case, it was because the url was malformed. Hope that helps someone out there.