#btn {
width: 96px;
height: 48px;
font-size: 24px;
}
function increment() {
btn.innerHTML++;
}
<!-- Enter your HTML code here -->
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<!-- HTML -->
<button id="btn" onclick="increment()">0</button>
</head>
<body>
<script src="js/button.js" type="text/javascript"></script>
</body>
</html>
