Javascript Helpers: Check variable is Number , Generic Ajax request , Serialize form data

Jscheats.js

//Check string is number
function isNumber(n) {
if(undefined == n || null == n)
   return false
else
 return /^-?[\d.]+(?:e-?\d+)?$/.test(n); 

} 


//Ajax request using plain javascript

var ajax = {};
ajax.x = function () {
    if (typeof XMLHttpRequest !== 'undefined') {
        return new XMLHttpRequest();
    }
    var versions = [
        "MSXML2.XmlHttp.6.0",
        "MSXML2.XmlHttp.5.0",
        "MSXML2.XmlHttp.4.0",
        "MSXML2.XmlHttp.3.0",
        "MSXML2.XmlHttp.2.0",
        "Microsoft.XmlHttp"
    ];

    var xhr;
    for (var i = 0; i < versions.length; i++) {
        try {
            xhr = new ActiveXObject(versions[i]);
            break;
        } catch (e) {
        }
    }
    return xhr;
};

ajax.send = function (url, callback, method, data, async) {
    if (async === undefined) {
        async = true;
    }
    var x = ajax.x();
    x.open(method, url, async);
    x.onreadystatechange = function () {
        if (x.readyState == 4) {
            callback(x.responseText)
        }
    };
    if (method == 'POST') {
        x.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
    }
    x.send(data)
};

ajax.get = function (url, data, callback, async) {
    var query = [];
    for (var key in data) {
        query.push(encodeURIComponent(key) + '=' + encodeURIComponent(data[key]));
    }
    ajax.send(url + (query.length ? '?' + query.join('&') : ''), callback, 'GET', null, async)
};

ajax.post = function (url, data, callback, async) {
    var query = [];
    for (var key in data) {
        query.push(encodeURIComponent(key) + '=' + encodeURIComponent(data[key]));
    }
    ajax.send(url, callback, 'POST', query.join('&'), async)
};


//Serialize form
function serialize(form) {
	if (!form || form.nodeName !== "FORM") {
		return
	}
	var i,	j,	q = [];
	for (i = form.elements.length - 1; i >= 0; i = i - 1) {
		if (form.elements[i].name === "") {
			continue
		}
		switch (form.elements[i].nodeName) {
		case "INPUT":
			switch (form.elements[i].type) {
			case "text":
			case "hidden":
			case "password":
			case "button":
			case "reset":
			case "submit":
				q.push(form.elements[i].name + "=" + encodeURIComponent(form.elements[i].value));
				break;
			case "checkbox":
			case "radio":
				if (form.elements[i].checked) {
					q.push(form.elements[i].name + "=" + encodeURIComponent(form.elements[i].value))
				}
				break;
			case "file":
				break
			}
			break;
		case "TEXTAREA":
			q.push(form.elements[i].name + "=" + encodeURIComponent(form.elements[i].value));
			break;
		case "SELECT":
			switch (form.elements[i].type) {
			case "select-one":
				q.push(form.elements[i].name + "=" + encodeURIComponent(form.elements[i].value));
				break;
			case "select-multiple":
				for (j = form.elements[i].options.length - 1; j >= 0; j = j - 1) {
					if (form.elements[i].options[j].selected) {
						q.push(form.elements[i].name + "=" + encodeURIComponent(form.elements[i].options[j].value))
					}
				}
				break
			}
			break;
		case "BUTTON":
			switch (form.elements[i].type) {
			case "reset":
			case "submit":
			case "button":
				q.push(form.elements[i].name + "=" + encodeURIComponent(form.elements[i].value));
				break
			}
			break
		}
	}
	return q.join("&")
};