How to Add Two Numbers in Javascript using Textbox

In this tutorial, you will learn how to add two numbers in javascript using textbox. This is a very basic thing that every newbie should be able to do without any issue.  But it is also tricky if you are trying to add 2 values that come from 2 different input fields.

Almost in every programming language, we have an addition operator (+) to get the sum of 2 numbers and it is also present in javascript. But since the value present in the input field is of string type, we have to convert it into number type using parseFloat() method and then do the calculation using addition operator (+).

In the following example, we have 2 input fields. In these fields, we will enter 2 random numbers and upon click of a button, we will get sum of these numbers and display it on the screen.  Please have a look over the code example and the steps given below.


  • We have 4 elements in the HTML file (div, input, button, and h1). The div element is just a wrapper for the rest of the elements.
  • The inner text for the button element is “Add” 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">
  <div class="container">
    <input type="number" id="firstInput">
    <input type="number" id="secondInput">

  <script src="script.js"></script>
.container {
    width: 400px;
    margin: auto;

input[type=number]::-webkit-outer-spin-button { 
  -webkit-appearance: none; 
  margin: 0; 


  • We have selected both the input elements, button element, and h1 element using the document.querySelector() method and stored them in firstInput, secondInput, btnAdd and result variables respectively.
  • We have attached the click event listener to the button element.
  • In the event handler function, we are passing values of both the input elements to the parseFloat() method and getting sum of them using the addition operator (+). The output is stored in the total variable.
  • We only want our result to be up to 3 decimal places and that is why we are using the toFixed() method and passing 3 as a parameter.
  • We are displaying the sum in the h1 element using the innerText property.
let firstInput = document.querySelector('#firstInput');
let secondInput = document.querySelector('#secondInput');
let btnAdd = document.querySelector('button');
let result = document.querySelector('h1');

btnAdd.addEventListener('click', () =>{
    let total = parseFloat(firstInput.value) + parseFloat(secondInput.value);
    result.innerText = total.toFixed(3);