Learn JavaScript Part 8: Function

<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <title></title>
</head>
<body>
    <div id="message">
        Sum =
    </div>

    <script id="javascript">
        function addition(value1, value2)
        {
            return value1 + value2;
        }
        var val1 = prompt("Enter Value1", "");
        var val2 = prompt("Enter Value2", "");
        document.getElementById('message').innerHTML += addition(Number(val1), Number(val2));
    </script>

</body>
</html>

User Input

Enter Value 1

10

Enter Value 2

20

Output

Sum = 30