# How to Use the isNaN() Function in JavaScript

09/30/2021

Contents

In this article, you will learn how to use the isNaN() function in JavaScript.

## Using the isNaN() Function in JavaScript

The isNaN() function is a built-in function in JavaScript that checks whether a value is NaN (Not a Number). It returns true if the value is NaN and false otherwise. The isNaN() function can be useful in various scenarios such as input validation, numeric calculations, and comparisons.

### Syntax

The syntax for the isNaN() function is as follows:

isNaN(value)

### Parameters

The isNaN() function takes only one parameter, which is the value to be checked. The value can be of any data type, but it is usually a number or a string that represents a number.

### Return value

The isNaN() function returns a Boolean value, true or false. If the value is NaN, it returns true. Otherwise, it returns false.

### Examples

Let’s look at some examples to understand how to use the isNaN() function in JavaScript.

#### Check if a value is NaN

let x = "Hello";
console.log(isNaN(x)); // Output: true

let y = 123;
console.log(isNaN(y)); // Output: false

In the above example, we have declared two variables x and y. The value of x is a string “Hello”, which is not a number, so the isNaN() function returns true. The value of y is a number, so the isNaN() function returns false.

#### Use isNaN() function in an if statement

let z = "ABC";
if (isNaN(z)) {
console.log("The value is not a number");
} else {
console.log("The value is a number");
}

In the above example, we have used the isNaN() function in an if statement to check whether the value of z is a number or not. Since z is not a number, the if condition is true, and the output is “The value is not a number”.