Editar o código:
ver o resultado »
Tente você mesmo - ©
w3ii.com
<!DOCTYPE html> <html> <body onbeforeunload="return myFunction()"> <p>Close this window, press F5 or click on the link below to invoke the onbeforeunload event.</p> <a href="../index.html">Click here to go to w3schools.com</a> <script> function myFunction() { return "Write something clever here..."; } </script> </body> </html>