Tryit Editor v2.7

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

<p>Click the button to open the dialog window.</p>

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

<p><b>Note:</b> The dialog element is only supported in Chrome 37+, Safari 6+ and Opera 24+.</p>

<dialog id="myDialog">This is an open dialog window</dialog>

<script>
function myFunction() {
    document.getElementById("myDialog").open = true;
}
</script>

</body>
</html>