Checking Types in JavaScript

* typeof operator

Type	Result
Undefined	"undefined"
Null	"object"
Boolean	"boolean"
Number	"number"
String	"string"
Host object (provided by the JS environment)	Implementation-dependent
Function object (implements [[Call]] in ECMA-262 terms)	"function"
Any other object	"object"

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

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* instanceof operator

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

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

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

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



출처 :
http://tobyho.com/2011/01/28/checking-types-in-javascript/
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/typeof
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/instanceof