JavaScript typeof operator

One of the JavaScript’s coolest functionality is to check the which type of object you have, It is helpful to you run time check which type of object this is and perform the according task on the object.

The typeof operator returns the string of evaluated object which indicates the which type of object this is.

Syntax

typeof <variable name or value>

Type	Result
Number	number
String	string
Boolean	boolean
Object	object
Function	function
Undefined	undefined
Null	object

var thisString = "String";
var thisNumber = 123;
var thisBoolean = false;

var thisFunction = function () {

}

var thisUndefined;

console.log("String Variable: " + typeof thisString);
console.log("Number Variable: " + typeof thisNumber);
console.log("Boolean Variable: " + typeof thisBoolean);
console.log("Function : " + typeof thisFunction);
console.log("Null " + typeof null);
console.log("Undefined: " + typeof thisUndefined);

Now run this script on you browser and checks the output on the browser’s console you will get the string returned by the typeof operator. You will get output like this:

Note: null keyword is also the object when you are checking any variable which currently null than it also return you the object. So it better you to check any object using the instanceof operator so it will return name of the class of that object.

alert(typeof null == "object"); // returns true

Some examples code:

//Numbers
typeof 13 === "number";
typeof NaN === "number";

//String
typeof "JavaScript" === "string";
typeof "" === "string";

//Boolean
typeof true === "boolean";
typeof false === "boolean";

//Object
typeof null === "object";
typeof { a: "a"} === "object"; // It is also called the plain object
typeof [4, 5, 6] === "object";
typeof new Date() === "object";

//Functions
typeof function () { } === "function";

see the instanceof operator

Happy Coding. 🙂