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.

• isNaN() Method
• isFinite() Method

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.

Example 2: In this example, we will check for some arguments if they are NaN or not.

Javascript

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

// It is not NaN
console.log(example(999));

// It is NaN
console.log(example('2C'));

Output:

It isnt NaN
It isnt NaN

Note: isNaN() (or Number.isNaN()) can be used to deduce if a number is NaN or not but it doesn’t says anything about the number being finite.

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