How to Create A Simple Calculator using JavaScript
Contents
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
<!DOCTYPE HTML>
<html lang="en">
<head>
<meta charset="utf-8">
<title>A Simple Calculator</title>
<link href="https://fonts.googleapis.com/css?family=Inconsolata" rel="stylesheet">
<style>
* {
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;
}
</style>
</head>
<body>
<div class="container">
<table border="1" cellspacing="0">
<tr>
<td colspan="4" id="inputLabel">0</td>
</tr>
<tr>
<td colspan="3"><button onclick="pushBtn(this);">AC</button></td>
<td><button onclick="pushBtn(this);">/</button></td>
</tr>
<tr>
<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>
</tr>
<tr>
<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>
</tr>
<tr>
<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>
</tr>
<tr>
<td colspan="2"><button onclick="pushBtn(this);">0</button></td>
<td><button onclick="pushBtn(this);">.</button></td>
<td><button onclick="pushBtn(this);">=</button></td>
</tr>
</table>
</div>
<script>
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;
}
}
}
</script>
</body>
</html>
