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<!DOCTYPE html> <html> <body> <p>Click the button to find out if the dialog window is open.</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> <p id="demo"></p> <dialog id="myDialog" open>This is an open dialog window</dialog> <script> function myFunction() { var x = document.getElementById("myDialog").open; document.getElementById("demo").innerHTML = x; } </script> </body> </html>