Simple, cross-browser Javascript POST/GET xhr request object. Supports request data and proper AJAX headers.

ajax.js

/**
 * IE 5.5+, Firefox, Opera, Chrome, Safari XHR object
 * 
 * @param string url
 * @param object callback
 * @param mixed data
 * @param null x
 */
function ajax(url, callback, data, x) {
	try {
		x = new(this.XMLHttpRequest || ActiveXObject)('MSXML2.XMLHTTP.3.0');
		x.open(data ? 'POST' : 'GET', url, 1);
		x.setRequestHeader('X-Requested-With', 'XMLHttpRequest');
		x.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
		x.onreadystatechange = function () {
			x.readyState > 3 && callback && callback(x.responseText, x);
		};
		x.send(data)
	} catch (e) {
		window.console && console.log(e);
	}
};


// https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest
// https://gist.github.com/jed/993585
// https://gist.github.com/Fluidbyte/5082377
// https://github.com/Xeoncross/kb_javascript_framework/blob/master/kB.js#L30
// https://gist.github.com/iwek/5599777
// http://msdn.microsoft.com/en-us/library/ms537505(v=vs.85).aspx#_id

// @todo look into lengthComputable for xhr.upload browsers
// http://stackoverflow.com/questions/11127654/why-is-progressevent-lengthcomputable-false
// http://stackoverflow.com/questions/10956574/why-might-xmlhttprequest-progressevent-lengthcomputable-be-false
// https://github.com/ForbesLindesay/ajax/blob/master/index.js

testing.ajax.js

/**
 * IE 5.5+, Firefox, Opera, Chrome, Safari XHR object
 * 
 * @param string url
 * @param object callback
 * @param mixed data
 * @param null x
 */
var ajax(url, callback, data, cache) {

    // Must encode data
    if(data && typeof(data) === 'object') {
        var y = '', e = encodeURIComponent;
        for (x in data) {
            y += '&' + e(x) + '=' + e(data[x]);
        }
        data = y.slice(1) + (! cache ? '&_t=' + new Date : '');
    }

    try {
        var x = new(this.XMLHttpRequest || ActiveXObject)('MSXML2.XMLHTTP.3.0');
        x.open(data ? 'POST' : 'GET', url, 1);
        x.setRequestHeader('X-Requested-With', 'XMLHttpRequest');
        x.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
        x.onreadystatechange = function () {
            x.readyState > 3 && callback && callback(x.responseText, x);
        };
        x.send(data)
    } catch (e) {
        window.console && console.log(e);
    }
};

ajax.uriEncode = function(o) {
    var x, y = '', e = encodeURIComponent;
    for (x in o) y += '&' + e(x) + '=' + e(o[x]);
    return y.slice(1);
};

ajax.collect = (a, f) {
    var n = [];
    for (var i = 0; i < a.length; i++) {
        var v = f(a[i]);
        if (v != null) n.push(v);
    }
    return n;
};

ajax.serialize = function (f) {
    function g(n) {
        return f.getElementsByTagName(n);
    };
    var nv = function (e) {
        if (e.name) return encodeURIComponent(e.name) + '=' + encodeURIComponent(e.value);
    };
    var i = collect(g('input'), function (i) {
        if ((i.type != 'radio' && i.type != 'checkbox') || i.checked) return nv(i);
    });
    var s = collect(g('select'), nv);
    var t = collect(g('textarea'), nv);
    return i.concat(s).concat(t).join('&');
};

// https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest
// https://gist.github.com/jed/993585
// https://gist.github.com/Fluidbyte/5082377
// https://github.com/Xeoncross/kb_javascript_framework/blob/master/kB.js#L30
// https://gist.github.com/iwek/5599777
// http://msdn.microsoft.com/en-us/library/ms537505(v=vs.85).aspx#_id

// @todo look into lengthComputable for xhr.upload browsers
// http://stackoverflow.com/questions/11127654/why-is-progressevent-lengthcomputable-false
// http://stackoverflow.com/questions/10956574/why-might-xmlhttprequest-progressevent-lengthcomputable-be-false

I like, just one thing, "data ? 'POST' : 'GET'" this will always become POST. Do the condiction check before instead, and set for example data to GET as default if not POST or GET is set, or just do some error handling about wrong type. I will modify and use, thanks.

If you want to use a synchronization request,
can not write
x.open(data ? 'POST' : 'GET', url, 0);
this will not work under > ie8 , must be
x.open(data ? 'POST' : 'GET', url, false);

@eduardoinnorway: I think you misunderstood the meaning of the data parameter. It is an optional Object of POST data. If it is undefined, the method will be GET.

but what if I want to make a get request with data? I would expect data would be serialized and passed as a query parameter on the url.

Why the x parameter???

@xeoncross would you mind popping a license on this?

What's the testing.ajax.js for?

Why the x parameter???

@nicdex It is a trick. It is just shorter to add a parameter than to write 'var x'. So it saves a few bytes at the cost of readability.

It's a nice trick if the intent is to golf the code but for readability it throws one off for a moment. Nice code though. I've "borrowed" your code and linked back to this in source code :)

Thanks man helps to me. To modify js ajax Request

I will go with
x.open(typeof data != 'undefined' ? 'POST' : 'GET', url, 1);
since sometime I need to send a POST with empty body