Simple type checking in JavaScript.

type.js

(function (root) {

    var type = function (o) {

        // handle null in old IE
        if (o === null) {
            return 'null';
        }

        // handle DOM elements
        if (o && (o.nodeType === 1 || o.nodeType === 9)) {
            return 'element';
        }

        var s = Object.prototype.toString.call(o);
        var type = s.match(/\[object (.*?)\]/)[1].toLowerCase();

        // handle NaN and Infinity
        if (type === 'number') {
            if (isNaN(o)) {
                return 'nan';
            }
            if (!isFinite(o)) {
                return 'infinity';
            }
        }

        return type;
    };

    var types = [
        'Null',
        'Undefined',
        'Object',
        'Array',
        'String',
        'Number',
        'Boolean',
        'Function',
        'RegExp',
        'Element',
        'NaN',
        'Infinite'
    ];

    var generateMethod = function (t) {
        type['is' + t] = function (o) {
            return type(o) === t.toLowerCase();
        };
    };

    for (var i = 0; i < types.length; i++) {
        generateMethod(types[i]);
    }

    if (typeof exports === "object" && exports) {
        exports = type;
    }
    else if (typeof define === "function" && define.amd) {
        define(type);
    }
    else {
        root.type = type;
    }

})(this);