Learn JavaScript Part 21: Extension Method

<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <title></title>
</head>
<body>
    <script id="javascript">
        String.prototype.getLength = function () {
            return this.length;
        }

        var str = "Akshay Patel";

        alert(str.getLength());
    </script>
</body>
</html>

Output

12