Read file:// URLs in IE XMLHttpRequest

Hmm, could it be the difference between the native XMLHttpRequest object and the ActiveX one? I seem to remember something about that. That is, instead of

var xhr = new XMLHttpRequest();

try

var xhr = new ActiveXObject("MSXML2.XMLHTTP");

Obviously, put some checks in place to see if the browser supports ActiveX. Of course, this is limited to IE only, as well.

How can I get code like this to work?

As suggested above, this looks like a fault in Microsoft XMLHttpRequest. jQuery (Jul 2011) also writes:-

Microsoft failed to properly implement the XMLHttpRequest in IE7 (can't request local files)

I confirm this failure for IE8 too.

A solution is to use new window.ActiveXObject( "Microsoft.XMLHTTP" ) for local files if XMLHttpRequest doesn't work.

The failure is in the xhr.open line so it can be caught there and then try ActiveXObject as follows:-

var xhr = new XMLHttpRequest()try {    xhr.open('GET', url, true)}catch(e) {    try {        xhr = new ActiveXObject('Microsoft.XMLHTTP')        xhr.open('GET', url, true)    }    catch (e1) {        throw new Error("Exception during GET request: " + e1)    }}

This code will at least use standard XMLHttpRequest for IE9 (untested) and future IE browsers if/when Microsoft fixes the fault. With the jQuery code above, non standard Microsoft.XMLHTTP will be used whenever ActiveXObject is available, even if Microsoft fix the fault.

I just happened to stumble across exactly the same problem. As suggested above, the non-native ActiveX "constructor" works. I’m not really sure whether there are different policies applied to the two objects, but since jQuery mentions the same problem as well, it may be a genuine bug. Here is the relevant piece of code from the jQuery source (1.4.2, line 4948):

// Create the request object; Microsoft failed to properly// implement the XMLHttpRequest in IE7 (can't request local files),// so we use the ActiveXObject when it is available// This function can be overriden by calling jQuery.ajaxSetupxhr: window.XMLHttpRequest && (window.location.protocol !== "file:" || !window.ActiveXObject) ?    function() {        return new window.XMLHttpRequest();    } :    function() {        try {            return new window.ActiveXObject("Microsoft.XMLHTTP");        } catch(e) {}    }