How to Check if a Value is a Number with JavaScript

In JavaScript, there are different ways to check whether a value is a number or something else.

The most common way is to use the typeof operator:

const value = 5

console.log(typeof value)
// "number"

One way you can use it in a practical context is to check if a form is filled out correctly, by using typeof in a conditional statement.

Let’s check if the value type of an input value is not a number value type, and then log out a message to the console:

const inputFieldAge = "10"
if (typeof inputFieldAge !== 'number') {
  console.log('This field has to be a number'
}

Because the inputFieldAge variable has a string assigned to it (the double quotes) instead of a number value type 10, the typeof operator will catch it.