What is JavaScript typeof Operator and its Examples

Nuelson Penuel Thursday, August 3, 2023 Javascript

JavaScript typeof Operator

The `typeof` operator in JavaScript is used to determine the type of a variable or expression. It returns a string that represents the data type.

JavaScript typeof Operator Syntax

typeof operand  
or  
typeof (operand)  


Examples of JavaScript typeof Operator

Here are some examples of the `typeof` operator in action:

Example 1: Checking a variable

let age = 25;
console.log(typeof age); // Output: "number"


In this example, the `typeof` operator is used to check the data type of the `age` variable, which is a number. The output will be the string "number".

Example 2: Checking a string

let name = "John";
console.log(typeof name); // Output: "string"


Here, the `typeof` operator is used to check the data type of the `name` variable, which is a string. The output will be the string "string".

Example 3: Checking an array

let numbers = [1, 2, 3, 4, 5];
console.log(typeof numbers); // Output: "object"


In this example, the `typeof` operator is used to check the data type of the `numbers` variable, which is an array. Arrays in JavaScript are considered as objects, so the output will be the string "object".

Example 4: Checking a boolean

let isActive = true;
console.log(typeof isActive); // Output: "boolean"


Here, the `typeof` operator is used to check the data type of the `isActive` variable, which is a boolean. The output will be the string "boolean".

Example 5: Checking an undefined value

let city;
console.log(typeof city); // Output: "undefined"


In this example, the `typeof` operator is used to check the data type of the `city` variable, which is currently undefined. The output will be the string "undefined".

Example 6: Checking a function

function sayHello() {
  console.log("Hello!");
}

console.log(typeof sayHello); // Output: "function"


Here, the `typeof` operator is used to check the data type of the `sayHello` function. Functions are considered as objects in JavaScript, so the output will be the string "function".

Example 7: Checking null

let address = null;
console.log(typeof address); // Output: "object"


In this example, the `typeof` operator is used to check the data type of the `address` variable, which has a value of `null`. Surprisingly, `typeof null` returns "object" instead of "null". This is a historical bug in JavaScript.

These are just a few examples of the `typeof` operator. It can be used to check the types of various other JavaScript constructs as well, such as objects, dates, and symbols.