Before building a calculator using JavaScript, you should have a basic understanding of HTML, CSS, and JavaScript. You should also have a text editor and a web browser installed on your computer.

Designing the calculator

The first step is to design the calculator’s user interface, which consists of the buttons and the output window. You can use HTML and CSS to create the calculator’s layout and styling.

htmlCopy code<div id="calculator">
  <input type="text" id="output">
  <!-- More buttons... -->

Styling the calculator

After designing the calculator’s layout, you can style it using CSS. You can use CSS to style the buttons, the output window, and the overall appearance of the calculator.

cssCopy code#calculator {
  border: 1px solid black;
  padding: 10px;
  display: inline-block;

#output {
  width: 100%;
  height: 40px;
  font-size: 24px;
  text-align: right;

button {
  width: 50px;
  height: 50px;
  font-size: 24px;
  margin: 5px;
  background-color: lightgray;
  border: none;
  border-radius: 5px;

Styling the Output Window

To display the result of the calculation, you need an output window. You can create a text field and style it using CSS to make it look like an output window.

htmlCopy code<input type="text" id="output">
cssCopy code#output {
  width: 100%;
  height: 40px;
  font-size: 24px;
  text-align: right;

The actual JavaScript

To make the calculator functional, you need to write JavaScript code. You can add event listeners to the calculator’s buttons, which trigger functions to perform calculations and update the output window.

jsCopy codeconst buttons = document.querySelectorAll('#calculator button');
const output = document.getElementById('output');

buttons.forEach(button => {
  button.addEventListener('click', () => {
    output.value += button.textContent;

This code adds a click event listener to each button in the calculator, which updates the output field with the button’s value.

The calculator functions

Here are some basic calculator functions that you can implement using JavaScript:

jsCopy codefunction add(a, b) {
  return a + b;

function subtract(a, b) {
  return a - b;

function multiply(a, b) {
  return a * b;

function divide(a, b) {
  if (b === 0) {
    return "Cannot divide by zero";
  return a / b;

You can use these functions to perform calculations based on the user input.

This is a basic outline for building a calculator using JavaScript. You can add more features and functionality based on your requirements.

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