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Best practice for AJAX / XmlHttpRequestSupport detection

I am trying to update an old JavaScript function used to detect AJAX support (i.e. XmlHttpRequest object). I have looked online (including SO) and found various solutions, but I'm not sure which is the most efficient one for simple support detection.

Current function:

    function IsSyncAJAXSupported()
    {
        var isSyncAJAXSupported = true;

        var xmlHttp = null;
        var clsids = ["Msxml2.XMLHTTP.4.0", "MSXML2.XMLHTTP", "Microsoft.XMLHTTP"];
        for(var i=0; i<clsids.length && xmlHttp == null; i++) {
            try {
                    xmlHttp = new ActiveXObject(clsids[i]);
            } catch(e){}
        }

        if(xmlHttp == null && MS.Browser.isIE)
        {
            isSyncAJAXSupported = false;
        }
        return isSyncAJAXSupported;
    }

In Firefox 3, the above gives errors because MS is undefined.

I understand that using the library would be better, but this is not a short term option. We only support IE6 and above + latest Firefox, Safari / WebKit and Opera.

What's the best way to get true / false support for XmlHttpRequest?

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3 answers


I came up with this:

var xhr = null;
try { xhr = new XMLHttpRequest(); } catch (e) {}
try { xhr = new ActiveXObject("Microsoft.XMLHTTP"); } catch (e) {}
try { xhr = new ActiveXObject("Msxml2.XMLHTTP"); } catch (e) {}
return (xhr!=null);


This seems to work, so I decided to share it.

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Not

Or rather, don't waste time doing what many other people have done.



Try grabbing the source jQuery or somesuch and "borrow" their methods; they've already invested time in supporting as many browsers as possible (especially with jQuery), so save time.

NTN

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My preferred code for this:

function CreateXMLHttpRequest()
{
  // Firefox and others
  try { return new XMLHttpRequest(); } catch (e) {}
  // Internet Explorer
  try { return new ActiveXObject("Microsoft.XMLHTTP"); } catch (e) {}
  try { return new ActiveXObject("Msxml2.XMLHTTP"); } catch (e) {}
  //alert("XMLHttpRequest not supported");
  // No luck!
  return null;
}

You can easily add tests for variants of Microsoft objects ...

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