How to check if a string is a number in javascript?

Hi Friends 👋,

Welcome To Infinitbility! ❤️

Today, I’m going to show how you check if a string is a number in javascript, here I will use the javascript isNaN() built-in method to check string is a valid number or not.

The isNaN() function determines whether a value is NaN (Not a number ) or not. Because coercion inside the isNaN function can be surprising, you may alternatively want to use Number.isNaN().

Let’s start today’s tutorial How to check if a string is a number in javascript?

First, let’s understand how the isNaN() method behaves, and what it returns in different input types.

Copy 
1isNaN(123)         // false
2isNaN('123')       // false
3isNaN('1e10000')   // false (This translates to Infinity, which is a number)
4isNaN('foo')       // true
5isNaN('10px')      // true
6isNaN('')          // false
7isNaN(' ')         // false
8isNaN(false)       // false

Understing the above one thing is clear, the isNaN() returns true if it’s string input.

So, what we will do.

1. Create a sample num string variable
2. Use isNaN() method to check valid number or not.
3. Console message if it’s a number

Copy 
1// Create a sample num string variable
2const numStr = "22";
3
4// Use `isNaN()` method to check valid number or not.
5if(!isNaN(numStr)){
6  // Console message if it's a number
7  console.log("numStr is a valid number");
8}

When running the above program it should console numStr is a valid number in the log. let’s check the output.

I hope it’s help you, All the best 👍.