How to display a string as teletype text using javascript?

Html page:

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

<p id="P16"></p>

Javascript page:

<script>

    function myFunction() {

        var str = "Hello World!";

        var result = str.fixed();

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

    }

</script>

Output:

Hello World!