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How to Create A Simple Calculator in JavaScript

How to Create A Simple Calculator using JavaScript



Introduction & Demo

In this video, I’ll show you how to create a simple calculator using JavaScipt!

Developing a calculator isn’t easy, but I make this super simple by using the eval() function. (The argument of this function is a string, and it executes a string as JavaScript code. Useful!)

Hope you enjoy coding!

Demo: Link


Sample Code

<html lang="en">
<meta charset="utf-8">
<title>A Simple Calculator</title>
<link href="" rel="stylesheet">
	* {
		font-family: 'Inconsolata', monospace;
		color: #555;
	body {
		background-color: #3fb399;
	.container {
		width: 320px;
		background-color: white;
		margin: 120px auto;
	table {
		width: 100%;
		border-color: #f4f4f4;
	td {
		width: 25%;
	button {
		width: 100%;
		height: 70px;
		font-size: 24px;
		background-color: white;
		border: none;
	#inputLabel {
		height: 120px;
		font-size: 40px;
		vertical-align: bottom;
		text-align: right;
		padding-right: 16px;
		background-color: #ececec;
<div class="container">
	<table border="1" cellspacing="0">
			<td colspan="4" id="inputLabel">0</td>
			<td colspan="3"><button onclick="pushBtn(this);">AC</button></td>
			<td><button onclick="pushBtn(this);">/</button></td>
			<td><button onclick="pushBtn(this);">7</button></td>
			<td><button onclick="pushBtn(this);">8</button></td>
			<td><button onclick="pushBtn(this);">9</button></td>
			<td><button onclick="pushBtn(this);">*</button></td>
			<td><button onclick="pushBtn(this);">4</button></td>
			<td><button onclick="pushBtn(this);">5</button></td>
			<td><button onclick="pushBtn(this);">6</button></td>
			<td><button onclick="pushBtn(this);">-</button></td>
			<td><button onclick="pushBtn(this);">1</button></td>
			<td><button onclick="pushBtn(this);">2</button></td>
			<td><button onclick="pushBtn(this);">3</button></td>
			<td><button onclick="pushBtn(this);">+</button></td>
			<td colspan="2"><button onclick="pushBtn(this);">0</button></td>
			<td><button onclick="pushBtn(this);">.</button></td>
			<td><button onclick="pushBtn(this);">=</button></td>

	var inputLabel = document.getElementById('inputLabel');
	function pushBtn(obj) {
		var pushed = obj.innerHTML;
		if (pushed == '=') {
			// Calculate
			inputLabel.innerHTML = eval(inputLabel.innerHTML);
		} else if (pushed == 'AC') {
			// All Clear
			inputLabel.innerHTML = '0';
		} else {
			if (inputLabel.innerHTML == '0') {
				inputLabel.innerHTML = pushed;
			} else {
				inputLabel.innerHTML += pushed;