Tryit Editor v2.9

Edit This Code:
<!DOCTYPE html>
<html>
<body>

<p>Click the button to open an output stream, add some text, and close the output stream.</p>

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

<script>
function myFunction() {
    document.open();
    document.write("<h1>Hello World</h1>");
    document.close();
}
</script>

</body>
</html>