By default, all objects that aren't Number, String, Boolean, Function, RegExp, Array, Date, or Error will return "Object" unless an optional second argument is passed.

/* JavaScript getClass - v0.1.0 - 10/27/2011
 * http://github.com/cowboy/javascript-getclass
 * Copyright (c) 2011 "Cowboy" Ben Alman; Licensed MIT, GPL */

(function (exports, global)
{
    'use strict';

    // A map of basic Object.prototype.toString output to [[Class]] names. This
    // serves the dual purpose of being the object on which the Object.prototype
    // .toString method is called.
    var classMap = {
        '[object Number]': 'Number',
        '[object String]': 'String',
        '[object Boolean]': 'Boolean',
        '[object Function]': 'Function',
        '[object RegExp]': 'RegExp',
        '[object Array]': 'Array',
        '[object Date]': 'Date',
        '[object Error]': 'Error'
    };

    // Return a specific useful value based on a passed object's [[Class]].
    exports.getClass = function (value, specific)
    {
        if (value === null)
        {
            // If the passed value is null, return "Null" (IE <= 8)
            return 'Null';
        }
        else if (value == null)
        {
            // If the passed value is undefined (the only value that
            // is == null but !== null is undefined), return 'Undefined'
            // (IE <= 8)
            return 'Undefined';
        }
        else if (specific && value === global)
        {
            // If in 'specific' mode, and the passed value is the global object,
            // return 'global'
            return 'global';
        }

        // Get the "[object [[Class]]]" string for the passed value.
        var key = classMap.toString.call(value);

        if (classMap.hasOwnProperty(key))
        {
            // If the key exists in classMap, return its [[Class]].
            return classMap[key];
        }
        else if (specific)
        {
            // If in "specific" mode, parse the [[Class]] value from
            // the string and return that.
            return key.slice(8, -1);
        }
        else
        {
            // If not in "specific" mode, just return the more generic "Object".
            return 'Object';
        }
    };
}(typeof exports === 'object' && exports || this, this));