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:

JavaScript typeof operator

JavaScript typeof operator

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. 🙂