How to Check if String is Decimal Number in Javascript

In this tutorial, you will learn how to check if string is decimal number in javascript. In a decimal number, the whole number part is separated from the fractional part using a decimal point or dot (.).

There are numerous ways to check if a string is a decimal number. We are going to use one of the easiest solutions which involve the usage of the match() method, parseFloat() method, isInteger() method, and ternary (?) operator. The ternary operator is also known as the conditional operator which acts similar to the if-else statement.

The match() methods matches a string against a regular expression. If the match is found, it returns an array of matches, otherwise returns null. The parseFloat() method takes a string as a parameter and returns a floating-point number. The isInteger() methods checks whether a variable is an integer or not.

In the following example, we have one global variable and upon click of a button, we will check if the string is a decimal 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 isDecimal() method and passing myVar as a parameter. This method will check if the string is a decimal number.
  • In the isDecimal(), we are using match() method, parseFloat() method, isInteger() method and ternary (?) operator to verify whether myVar is a decimal number or not. This method returns a boolean value.
  • Depending upon the result of the check, 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 = "6.5444000";

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

function isDecimal(str) {
  let pattern = /^-?\d*(\.\d+)?$/;
  if (!str.match(pattern)) return false;
  let val = parseFloat(str);
  const isInteger = Number.isInteger(val);
  return isInteger ? false : true;