typeof

Baseline Widely available

This feature is well established and works across many devices and browser versions. Its been available across browsers since 20157.

typeof , (unevaluated)


:	JavaScript 1.1
ECMA :	ECMA-262 ( ECMA-357 for E4X objects)


Undefined	`"undefined"`
Null	`"object"`
Boolean	`"boolean"`
Number	`"number"`
String	`"string"`
( JS )
Function ( ECMA-262 [[Call]])	`"function"`
E4X XML	"xml"
E4X XMLList	"xml"
	`"object"`

// Numbers
typeof 37 === "number";
typeof 3.14 === "number";
typeof Math.LN2 === "number";
typeof Infinity === "number";
typeof NaN === "number"; //  "Not-A-Number"
typeof Number(1) === "number"; // !

// Strings
typeof "" === "string";
typeof "bla" === "string";
typeof typeof 1 === "string"; // typeof 
typeof String("abc") === "string"; // !

// Booleans
typeof true === "boolean";
typeof false === "boolean";
typeof Boolean(true) === "boolean"; // !

// Undefined
typeof undefined === "undefined";
typeof blabla === "undefined"; //  undefined 

// Objects
typeof { a: 1 } === "object";
typeof [1, 2, 4] === "object"; //  Array.isArray  Object.prototype.toString.call 
typeof new Date() === "object";

typeof new Boolean(true) === "object"; // !
typeof new Number(1) === "object"; // !
typeof new String("abc") === "object"; // !

// Functions
typeof function () {} === "function";
typeof Math.sin === "function";

`null`

typeof null === "object"; //  JavaScript

JavaScript , JavaScript 0. null NULL ( 0x00) . , null 0 , typeof . ()

ECMAScript ( opt-in ). typeof null === 'null'

(Regular expressions)

(need reference to say which).

typeof /s/ === "function"; // Chrome 1-12 ... //  ECMAScript 5.1 (:  Chrome  'object')
typeof /s/ === "object"; // Firefox 5+ ...    //  ECMAScript 5.1