How to convert the string to uppercase letters global using

Html page:

<button onclick="myFunction()">Try it</button>

<p id="P11"></p>

Javascript page:

<script>

    function myFunction()

    {

        var str = "Hello World!";

        var res = str.toUpperCase();

        document.getElementById("demo").innerHTML = res;

    }

</script>

Output:

HELLO WORLD!