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How to check if a value is a number in JavaScript

Published Jun 21 2020

We have various ways to check if a value is a number.

The first is isNaN(), a global variable, assigned to the window object in the browser:

const value = 2

isNaN(value) //false

isNaN('test') //true

isNaN({}) //true

isNaN(1.2) //false

If isNaN() returns false, the value is a number.

Another way is to use the typeof operator. It returns the 'number' string if you use it on a number value:

typeof 1 //'number'

const value = 2

typeof value //'number'

So you can do a conditional check like this:

const value = 2
if (typeof value === 'number') {
  //it's a number
}


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