How to Check if String is a Whole Number in Javascript

In this tutorial, you will learn how to check if string is a whole number in javascript. A number is considered to be a whole number if it is greater than or equal to 0.

There are numerous ways to check if a string is a whole number. We are going to use one of the easiest solutions which involve the usage of the isInteger() method and ternary (?) operator.  The isInteger() methods checks whether a variable is an integer or not. The ternary operator is also known as the conditional operator which acts similar to the if-else statement.

In the following example, we have one global variable and upon click of a button, we will check if the string is a whole number and display the result on the screen.  Please have a look over the code example and the steps given below.


  • We have 3 elements in the HTML file (div, button, and h1). The div element is just a wrapper for the rest of the elements.
  • The innerText for the button element is “Check” and for the h1 element, 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">

    <script src="script.js"></script>
body {
    text-align: center;

div {
    display: inline-block;

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


  • We have selected the button element and h1 element using the document.querySelector() method and stored them in btnCheck and output variables respectively.
  • We have a global variable myVar which holds a string as its value.
  • We have attached a click event listener to the button element.
  • In the event handler function, we are calling isWholeNumber() method and passing myVar as a parameter. This method will verify if the string is a whole number and will return either true or false.
  • In the isWholeNumber() method, we are checking if myVar is an integer and whether it is greater than or equal to 0.
  • Depending upon the returned value, we will assign “Yes” or “No” to the result variable.
  • We are displaying the result in the h1 element using the innerText property.
let btnCheck = document.querySelector("button");
let output = document.querySelector("h1");

let myVar = "5";

btnCheck.addEventListener("click", () => {
  let result = isWholeNumber(myVar) ? "Yes" : "No";
  output.innerText = result;

function isWholeNumber(str) {
  const num = Number(str);
  return Number.isInteger(num) && num >= 0;