Check if the dialog is currently open.
Examples
sample
<div id="dialog" style="display: none">Lorem ipsum dolor sit amet, consectetur adipiscing elit...</div>
<button onclick="dialog.open()">Open Dialog</button>
<button onclick="dialog.close()">Close Dialog</button>
<button onclick="alert($('#dialog').dialog('isOpen'))">isOpen</button>
<script>
var dialog = $('#dialog').dialog();
</script>