How to capture the status (and readyState) of XHR from IE6?

I'm not sure, but I suppose the problem is that due to "Ajax" in Internet Explorer 6, 7 and 8 (the latter two if used in quirks-mode ) use ActiveX instead of% w / o itself, you should do the correct "ActiveX" check, in case you have XMLHttpRequest and Microsoft.XMLHTTP .

  

A very important detail is that you should always use XHR in Msxml2.XMLHTTP pages, ie using http:// may fail.

So if you want to give some support for IE6 and 7/8 use this:

function XHR() {
    if (window.XMLHttpRequest) {
        return new window.XMLHttpRequest;
    } else if (window.ActiveXObject) {
        try {
            return new window.ActiveXObject("Msxml2.XMLHTTP");
        } catch (e1) {
            return false;
        }

        try {
            return new window.ActiveXObject("Microsoft.XMLHTTP");
        } catch (e1) {
            return false;
        }
     }
 }

A detail that in modern browsers does not affect, but in some of the old ones it was the problem with the order of the methods call, so I always used the following orderm, file:/// , .open (or directly .onreadystatechange ) and .readyState .

The use of the code would be something like (read about .send ):

var foo = XHR();

foo.open("GET", "/url", true); //Usa chama assíncrona

//Use o readyState após o .open, como já dito
foo.onreadystatechange = function() {

    switch (foo.readyState) {
        case 0:
            //(não inicializado)
        break;
        case 1:
            //(carregando)
        break;
        case 2:
            //(já carregado)
        break;
        case 3:
            //(interativo)
        break;
        case 4:
            //(completo) ... Neste ponto já se pode chamar o responseText

            alert(foo.responseText);
        break;
    }
};

//Faz a requisição
foo.send(null);

An example with other Activex (I've developed a lot for IEs and the previous code worked since IE5.01 +):

function XHR() {
    if (window.XMLHttpRequest) {
        return new window.XMLHttpRequest;
    }

    var XMLHttpFactories = [
        "Msxml3.XMLHTTP", "Msxml2.XMLHTTP", "Microsoft.XMLHTTP"
    ];

    var obj = false, i = 0, j = XMLHttpFactories.length;

    for (; i < j; i++) {

        try {
            obj = new window.ActiveXObject(XMLHttpFactories[i]);
        } catch (e) {
            continue;
        }

        break;
    }

    return obj;
}

  

Note: The .readyState is expendable, I only used it to avoid conflicts with variables in other scopes, which may be almost impossible but is only to avoid.

A tip, you'd rather avoid (never use) sync mode:

foo.open("GET", "/url", false);

Look at this line:

var xhr = window.XMLHttpRequest ? new XMLHttpRequest :

Notice something wrong? You forgot the parentheses! The correct would be this:

var xhr = window.XMLHttpRequest ? new XMLHttpRequest() :