typeof 3 // "number"
typeof "abc" // "string"
typeof {} // "object"
typeof true // "boolean"
typeof undefined // "undefined"
typeof function(){} // "function"

typeof [] // "object"

typeof null // "object"

function Animal(){}
var a = new Animal()
a instanceof Animal // true

a.constructor === Animal // true

function Cat(){}
Cat.prototype = new Animal()
Cat.prototype.constructor = Cat
var felix = new Cat()
felix instanceof Cat // true
felix instanceof Animal // true
felix.constructor === Cat // true
felix.constructor === Animal // false

felix = null
felix instanceof Animal // true
felix.constructor === Animal // throws TypeError

[1, 2, 3] instanceof Array // true
/abc/ instanceof RegExp // true
({}) instanceof Object // true
(function(){}) instanceof Function // true

3 instanceof Number // false
true instanceof Boolean // false
'abc' instanceof String // false

null instanceof Boolean // false
undefined instanceof Array // false

(3).constructor === Number // true
true.constructor === Boolean // true
'abc'.constructor === String // true

var wrapper = new Number(3)

new Number(3) instanceof Number // true
new Boolean(true) instanceof Boolean // true
new String('abc') instanceof String // true

var iframe = document.createElement('iframe')
document.body.appendChild(iframe)
var iWindow = iframe.contentWindow // get a reference to the window object of the iframe
iWindow.document.write('<script>var arr = [1, 2, 3]</script>') // create an array var in iframe's window
iWindow.arr // [1, 2, 3]
iWindow.arr instanceof Array // false

Array === iWindow.Array // false

iWindow.arr instanceof iWindow.Array // true

// source: http://forums.devshed.com/javascript-development-115/javascript-test-whether-a-variable-is-array-or-not-33051.html
function isArray(obj){
    return (typeof(obj.length)=="undefined") ?
        false:true;
}

 
또는 
 
// source: http://www.hunlock.com/blogs/Ten_Javascript_Tools_Everyone_Should_Have
function isArray(testObject) {
    return testObject &&
	!(testObject.propertyIsEnumerable('length')) &&
	typeof testObject === 'object' &&
	typeof testObject.length === 'number';
}

isWindow: function( obj ) {
    return obj && typeof obj === "object" && "setInterval" in obj;
}

$.isWindow({setInterval: 'bah!'}) // true

Object.prototype.toString.call(3) // "[object Number]"
Object.prototype.toString.call([1, 2, 3]) // "[object Array]"
Object.prototype.toString.call({}) // "[object Object]"

Object.prototype.toString.call(new Animal) // "[object Object]"

Object.prototype.toString.call(iWindow.arr) === "[object Array]" // true

var pWindow = open("")
pWindow.document.write('<script>var arr = [1, 2, 3]</script>')
Object.prototype.toString.call(pWindow.arr) // IEd에선 "[object Object]" 반환한다. 다른 브라우저는 "[object Array]"를 반환

Function.prototype.toString.call((3).constructor)
// "function Number() {
//    [native code]
// }"

function type(obj){
	var text = Function.prototype.toString.call(obj.constructor)
	return text.match(/function (.*)\(/)[1]
}
type("abc") // "String"

type(new Animal) // "Animal"

function type(obj){
	var text = obj.constructor.toString()
	return text.match(/function (.*)\(/)[1]

Array.toString = function(){ return "function NotArray(){ }" }
type([1,2,3]) // "NotArray"

var f = function Animal(){ "something" }
 
var g = function Animal(){ "something entirely different" }
type(new f) // "Animal"
type(new g) // "Animal"

> var div = document.createElement('div')
> typeof div
Safari 5.0 => object
Firefox 3.6 => object
IE 7.0 => object
IE 8.0 => object
Opera 11.01 => object
> div instanceof Element
Safari 5.0 => true
Firefox 3.6 => true
IE 7.0 => Error: 'Element' is undefined
IE 8.0 => true
Opera 11.01 => true
> div instanceof HTMLDivElement
Safari 5.0 => true
Firefox 3.6 => true
IE 8.0 => true
IE 7.0 => Error: 'HTMLDivElement' is undefined
Opera 11.01 => true

> Object.prototype.toString.call(div)
Safari 5.0 => [object HTMLDivElement]
Firefox 3.6 => [object HTMLDivElement]
IE 7.0 => [object Object]
IE 8.0 => [object Object]
Opera 11.01 => [object HTMLDivElement]

> div.constructor.toString()
Safari 5.0 => [object HTMLDivElementConstructor]
Firefox 3.6 => [object HTMLDivElement]
IE 7.0 => Error: 'div.constructor' is null or not an object
IE 8.0 => [object HTMLDivElement]
Opera 11.01 => function HTMLDivElement() { [native code] }

> typeof window
Safari 5.0 => object
Firefox 3.6 => object
IE 8.0 => object
IE 7.0 => object
Opera 11.01 => object
> window instanceof Window
Safari 5.0 => ReferenceError: Can't find variable: Window
Firefox 3.6 => true
IE 8.0 => true
IE 7.0 => Error: 'Window' is undefined
Opera 11.01 => ReferenceError: Undefined variable: Window
> Object.prototype.toString.call(window)
Safari 5.0 => [object DOMWindow]
Firefox 3.6 => [object Object]
IE 8.0 => [object Object]
IE 7.0 => [object Object]
Opera 11.01 => [object Window]
> window.constructor
Safari 5.0 => function Object() {
    [native code]
}
Firefox 3.6 => function Object() {
    [native code]
}
IE 8.0 => [object Window]
IE 7.0 => undefined
Opera 11.01 => function Object() { [native code] }