XMLHttp

Trying to fail gracefully in old Explorer

[dcrombie]

I've been doing some work using XMLHttp but the JS code errors in Explorer 5.5 (Windows) and 5.2 (Mac). It seems to work as expected in Explorer 6.0 (Windows). Anyone have an option short of browser-sniffing?!?

var req; 
 function loadXMLDoc(url) 
 { 
  if(window.XMLHttpRequest) { 
   // code for Gecko/KHTML browsers 
  } else if(window.ActiveXObject) { 
==> execution gets to here, then errors on next line 
   if(req = new ActiveXObject("Microsoft.XMLHTTP")) { 
    // code for Explorer 
   } 
  } 
 }

[dcrombie]

Found the solution:

try { 
    req = new ActiveXObject("Microsoft.XMLHTTP"); 
   } 
   catch(e) { 
    req = new ActiveXObject("Msxml2.XMLHTTP"); 
   }

;)

[Bernard Marx]

You could spread the net further:

function getXMLHttp()
{
    var xml;
    try
    {
        // Mozilla Browsers
        xml = new XMLHttpRequest();
        return xml;
    }
    catch(e){}
    
    // IE Browsers
    var progIDs = ["MSXML2.XMLHttp.5.0","MSXML2.XMLHttp.4.0","MSXML2.XMLHttp.3.0","MSXML2.XMLHttp","Microsoft.XMLHttp"];
    for(var currentProgID = 0;currentProgID < progIDs.length;currentProgID++)
    {
        try
        {
            xml = new ActiveXObject(progIDs[currentProgID]);      
            return xml;
        }
        catch(e){}
    }
}

[dcrombie]

Jeepers! I didn't realise it was such a mess - are there actually browsers that only support, for example, "MSXML2.XMLHttp.5.0" and not "MSXML2.XMLHttp" or "Microsoft.XMLHttp"?

I assume "MSXML2.XMLHttp" came first and the numerical suffixes indicate more recent versions (like JavaScript1.2 et. al.)?

[Bernard Marx]

I'm probably more in the dark than you are here. I got that list in the array from a friend. Here's some MS info that might explain it all:
[msdn.microsoft.com...]

[dcrombie]

[msdn.microsoft.com...]

Currently, the default XML parser for Internet Explorer is MSXML 2.0 or MSXML 3.0, depending on the version of Internet Explorer. With the help of the xmslinst.exe utility, you can change the default parser to MSXML 2.6 or MSXML 3.0. However, this can often cause unintended side-effects for some applications. Therefore, such a practice is not enabled for MSXML versions 4.0 and later....

I think that means you can leave off the numeric extensions and Explorer will use it's default.

[Bernard Marx]

Ah good stuff. That'll certainly make the code shorter!