JavaScript external_js
<html>
<head>
<script src="myjs.js">
</script>
</head>
<body>
<input type="button" onClick="popup()" value="Click Me!">
</body>
</html>
<head>
<script src="myjs.js">
</script>
</head>
<body>
<input type="button" onClick="popup()" value="Click Me!">
</body>
</html>
Result
