How to Use the isNaN() Function in JavaScript

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”.