JavaScript Type Determination

The tables below show some common types of objects and what they appear to be via different mechanisms in your browser:

** NO JavaScript Enabled **

Simple Objects/Variables

Object / Code typeof a a.toString() Expected instanceof 
var a = true;
 
Boolean
 
var a = false;
 
Boolean
 
var a = 10;
 
Number
 
var a = 10.0;
 
Number
 
var a = "10.0";
 
String
 
var a = "hello world";
 
String
 
var a = 'hello world';
 
String
 
var a = 'c';
 
String
 
var a = [];
 
Array
 
var a = [1,2,3];
 
Array
 
function getArguments(){
  return arguments;
}
var a = getArguments();
 
Array
 
function getArguments(foo, bar, baz){
  return arguments;
}
var a = getArguments(1,2,3);
 
Array
 
function getArguments(){
  return arguments;
}
var a = getArguments(1,2,3);
 
Array
 
var a = {};
 
Object
 
var a = {
  foo: 10,
  bar: "baz",
  isAlive: false
};
 
Object
 
var a = function(){};
 
Function
 
var a = function(){
  console.log("in function a");
};
 
Function
 
function a(){};
 
Function

Built-in Complex-ish Types and Other Stuff

Object / Code typeof a a.toString() Expected instanceof 
var a = new String();
 
String
 
var a = new Array();
 
Array
 
var a = new Date();
 
Date
 
var a = Math;
 
Object
 
var a = /^$/;
 
RegExp
 
var a = new RegExp("^$");
 
RegExp
 
var a = setTimeout(function(){}, 100);
 
Number

DOM Objects

Object / Code typeof a a.toString() Expected instanceof 
var a = document;
 
HTMLDocument
 
var a = window;
 
Window
 
var a = navigator;
 
Navigator
 
var a = document.createElement("table");
 
HTMLTableElement
 
var a = document.createElement("div");
 
HTMLDivElement
 
var a = document.createElement("p");
 
HTMLParagraphElement
 
var a = document.createElement("h1");
 
HTMLHeadingElement
 
var a = document.createElement("h2");
 
HTMLHeadingElement
 
var a = document.createElement("object");
 
HTMLObjectElement
 
var a = document.createElement("embed");
 
HTMLEmbedElement
 
var a = document.createElement("script");
 
HTMLScriptElement
 
var a = document.createElement("style");
 
HTMLStyleElement

Class Objects

Object / Code typeof a a.toString() Expected instanceof 
function MyClass(){}
var a = new MyClass();
 
MyClass
 
function MyClass(){}
var a = MyClass.prototype;
 
Object
 
function MyClass(){
    this.fn = function(){};
}
var b = new MyClass();
var a = b.fn;
 
Function
 
function MyClass(){
}
MyClass.prototype.fn = function(){};
var b = new MyClass();
var a = b.fn;
 
Function
 
var myObj = {
    fn: function(){}
}
var a = myObj.fn;
 
Function

Null/Undefined and Error Objects

Object / Code typeof a a.toString() Expected instanceof 
var a = null;
 
Object
 
var a = undefined;
 
Object
 
// leave empty
 
Object
 
var a = new Error("Uh Oh.");
 
Error