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[Geppetto Luis]

View message ALERT !!! for 3 seconds

then you must close automatically.

[JJMack]

Alert messages require user interaction the script is suspended till the Alert is acknowledged.  You may be able to use ScriptUI to display a message in a window or a countdown progress window for seconds then close the UI window.  The user may or may not see the message it depend where their eyes are for those seconds.

[sidpalas]

It seems that this Stack Overflow post​ is close to what OP wanted, except that per the Javascript Tools Guide "Adobe Photoshop does not support script creation of palette windows"

If you change the type of window to be a "dialog" instead of a "palette", the window does show up, but then I think it stops the execution of the delay function and causes PS to freeze (at least when I tested it...).

[Geppetto Luis]

thank you