step1-helloworld.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <script>
        // window.onload = init;
        window.addEventListener("load", init);
        function init(){
            document.getElementsByTagName("h1")[0].innerHTML = "Hello World";
        };
    </script>
</head>
<!-- body onload="init()"-->
<body>
    <!-- h1 id="display"></h1>
    <script>
        document.getElementById("display").innerHTML = "Hello World";
    </script-->
     <!--h1 class="display"></h1>
    <script>
        document.getElementsByClassName("display")[0].innerHTML = "Hello World";
    </script -->
    <h1></h1>
</body>
</html>