How to check if a value is a number using JavaScript

In JavaScript, there are a lot of ways to check if a value is a number or not. But, in this article, I will try to explain some of these.

We will use the typeof operator and the isNaN() method to check if a value is a number.

const myText = 5 ;
if (typeof myText === 'number') {
  alert ('Yes! This is a number.');
} else {
   alert('Not a number');
}

[1] Check a number using the typeof operator. #

typeof operator returns number if the value is a number. If the value is a string, it returns string.

For example,

1. We create a variable and set its value to 5.
   

   const myText = 5

2. Then use the typeof operator to check the variable. e.g.
   

    console.log(typeof myText);
   
   // output => number

   I have use the console.log method to print the output to the console.
3. In the second example, we will create one more variable and set its value a string. e.g.
   

   const myText = "Our Schools"

4. Now, if we check the variable using the typeof operator, it will return string.
   

    console.log(typeof myText);
   
   // output => string

typeof operator also returns the following data type.

typeof operator also returns the the following data type. But, in this article, we will ignore them.

console.log(typeof false);// output => boolean
console.log(typeof [1,2,3,4]);// output => object
console.log(typeof new Date());// output => object
console.log(typeof function() {});// output => function
console.log(typeof null);// output => object
console.log(typeof newVar);// output => undefined  *(not assigned)

I hope with the above example I have made you understand the usage of typeof operator.

Now, you have understood that if you want to do something after checking a value, you have to use the if/else statement. For example -

1. Let create a variable with its value 5. e.g.
   

   const myText = 5

2. In the above example, you have seen if we use the typeof operator to check a variable, it returns string or number. So, we will use the if/else statement to add a condition, if the variable myText is equal to number, we will alert Yes! This is a number., otherwise we will alert Not a number. using the alert() method. e.g.

if (typeof myText === 'number') {
  alert('Yes! This is a number.');
} else {
   alert('Not a number');
}

[2] Check a value using the isNaN() method. #

We can also use the isNaN() method to check a value is a number or not.

Syntax :

isNaN(value)

The isNaN() method returns true if a value is not a number, otherwise it returns false. e.g.

const myText = "String";
console.log(isNaN(myText))
 // output => true

  const myText = 5;
  
  if (isNaN(myText)){
  alert('Not a number');
} else {
  alert('Yes! This is a number.');
}

Conclusion #

In this article, you have learned How to check if a value is a number using JavaScript typeof operator and isNaN() method.