How to check if variable is a number in JavaScript (NaN, typeof, regex)

There are multiple ways to can check if a given variable (var) is a number or not in JavaScript. Let us take a look at a few of them with examples.

Example 1: Using typeof operator

var variable = 22.5;

if (typeof variable === 'number') {
    console.log('The variable is a number!');
} else {
    console.log('The variable is not a number!');
}

Output:
The variable is a number!

Documentation:



typeof operator returns a string indicating the type of the operand's value.
Example 1: console.log(typeof 101);
Output: number
Example 2: console.log(typeof "Mike");
Output: string
Link: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/typeof

Example 2: Using Number.isNaN()

var variable = "hello";

if (!Number.isNaN(variable)) {
    console.log('The variable is a number!');
} else {
    console.log('The variable is not a number!');
}

Documentation:



Number.isNaN() is a static method that can be used to identify if the value is the number value NaN (Not a Number), and returns false if the input is not of the Number type.
Link: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/isNaN

Example 3: Using Regular Expression

var variable = 100;
const regexStr = "/^-?\d+(\.\d+)?$/";
if (regexStr.test(variable)) {
    console.log('The variable is a number.');
} else {
    console.log('The variable is not a number.');
}