How to Check Whether a Number is Decimal or Not in Javascript

In this tutorial, you will learn how to check whether a number is decimal or not in javascript. A number whose whole number part and fraction part is separated by decimal point is known as a decimal number. We have float primitive type to handle decimal numbers in javascript.

There are numerous ways to detect if a number is a decimal number or not, but I am going to share one of the simplest methods. This method involves the usage of the parseFloat() method and modulus operator (%).

The parseFloat() method will take a string as a parameter and return a floating-point number.  It may or may not have decimal because it depends if a string contains a whole number or decimal number. The modulus operator (%) returns the remainder of a division.

In the following example, we are going to enter a decimal number in the input field and use a combination of parseFloat() method and modulus operator (%) to detect whether the number is a decimal or not.  Depending upon the result, we will display a Boolean value on the screen.  Please have a look over the code example and steps given below.


  • We have 4 elements in the HTML file and that includes div, input, button, and h1 elements.
  • The div element is just a wrapper for the rest of the elements.
  • The inner text for the button element is “Get” and for the h1 button, it is “Result”.
  • We have done some basic styling using CSS and added the link to our style.css stylesheet inside the head element.
  • We have also included our javascript file script.js with a script tag at the bottom.
<!DOCTYPE html>
<html lang="en">
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <link rel="stylesheet" href="style.css">
        <input type="number">
    <script src="script.js"></script>
div {
    text-align: center;

input, button {
    display: inline-block;
    padding: 10px 20px;


  • We have selected button, input, and h1 elements using document.querySelector() and stored them in btnGet, input, and result variables respectively.
  • We have attached the click event listener to the button element.
  • In the event handler function, we are using the parseFloat() method and passing the value of the input element to convert the string to a decimal number. We are storing the returned value in the num variable.
  • We have to divide num by 1 and get the remainder. To achieve that, we are using the modulus operator (%).  If the remainder is 0, that means the number is a whole number. Otherwise, it is a decimal number.  This calculation results in a Boolean value.
  • We are displaying that Boolean value in the h1 element.
let btnGet = document.querySelector('button');
let input = document.querySelector('input');
let result = document.querySelector('h1');

btnGet.addEventListener('click', () => {
    let num = parseFloat(input.value);
    result.innerText = num % 1 != 0 ? 'True' : 'False';