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

When working with numbers in JavaScript, it's important to know how to determine if a value is NaN (Not-a-Number) or finite. This knowledge is crucial for data validation, error handling, and ensuring your code behaves as expected. 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.

Methods to Check if a Number is NaN or Finite

JavaScript offers several built-in methods to check if a number is NaN or finite:

Using isNaN() Method

The isNaN() function checks whether a value is NaN. It’s a boolean function that returns true if the value is NaN and false otherwise. This function tries to convert the input into a number before checking, which can sometimes lead to unexpected results when working with non-numeric values.

Syntax:

isNan(parameter);

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

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'));

It isnt NaN
It is NaN

Note: For a more reliable check that avoids type coercion, use Number.isNaN(). This method only returns true if the value is actually NaN and not just something that can't be coerced into a number.

Using isFinite() Method

The isFinite() function checks if a number is finite. A finite number is one that is not Infinity, -Infinity, or NaN. This method converts the input to a number first, so it can return true for strings that can be converted to finite numbers.

Syntax:

isFinite(parameter);

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

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

Number is not finite
Number is finite

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.

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.

// 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