Countdown timer in seconds for a site with a browser pop-up message at the end of the timer.

The timer counts down seconds in real time, in reverse order to "0".
After the timer expires, a pop-up browser dialog box (Alert) is displayed with the message specified in the settings.

--------- Timer setting: ---------

- timer time in seconds, such as 10, 30, 60, 120 seconds, etc.
- message text.

--------- Advantages: ---------

- open source.
- without binding to the domain.
- does not depend on jQuery version.