How to check whether a number is NaN or finite in JavaScript ?

In this article, we will see how to check whether the number is NaN or finite. To check whether the given number is NaN or finite, we can use JavaScript methods.

These are the following methods for solving this problem:

Using isNaN() Method

To determine whether a number is NaN, we can use the isNaN() function. It is a boolean function that returns true if a number is NaN otherwise returns false.

Syntax:

isNan(parameter);

Example 1: This method shows the usage of the Javascript isNan() method.

Javascript

function example(x) {
    if (isNaN(x)) {
        return 'It is NaN';
    } else {
        return 'It isnt NaN';
    }
}

// It is not NaN
console.log(example(13));

// It is NaN
console.log(example('GeeksForGeeks'));

Output:

It isnt NaN
It is NaN

Note: The isNaN() function can alternatively be used as Number.isNaN(). It is considered to be a more robust version of the original.

Using isFinite() Method

To determine whether a number is finite we can use the isFinite() function. It is a boolean function that returns true if a number is Finite otherwise false.

Syntax:

isFinite(parameter);

Example 1: This method shows the use of the isFinite() method in Javascript.

Javascript

function example(x) {
    if (isFinite(x)) {
        return 'Number is finite';
    }
    return 'Number is not finite';
}

console.log(example('2021/10/29'));
// Number is not finite

console.log(example(29));
// Number is finite

Output:

Number is not finite
Number is finite

Example 2: In this example, we will check for numbers if they are finite or not.

Javascript

function example(x) {
    if (isFinite(5 / x)) {
        return 'Number is finite';
    }
    return 'Number is not finite';
}

console.log(example(0));
// Number is not finite

console.log(example(10));
    // Number is finite

Output:

Note: If needed, the isFinite() function can parse the parameter into the number

Example 3: In this example, we will check for numbers if they are finite or not using the isFinite() method of Javascript.

Javascript

function example(x) {
    if (isFinite(x)) {
        return 'Number is finite';
    }
    return 'Number is not finite';
}

console.log(example('123'));
// Number is finite

console.log(example(133));
// Number is finite

console.log(example('123D'));
// Number is not finite

Output:

Number is finite
Number is finite
Number is not finite

Using Lodash isFinite() and _.isNaN() Methods

In this example, we are using Lodash’s function to check whether the given number is finite or NaN.

Example: This example shows the implementation of above- explained approach.

Javascript

// Defining Lodash variable
const _ = require('lodash');

let a = 10;
if (_.isFinite(a)) console.log(" it is a finite number");
if (_.isNaN(a)) console.log(" It is NaN")

Output:

 it is a finite number