How to capture browser tab/window close event in 4GL program?

The OPTIONS ON TERMINATE SIGNAL can be used to catch the close tab/browser event in 4GL program.

Below is an example program to demonstrate the subject functionality:

DATABASE test1

MAIN
    DEFINE cnt INTEGER

    OPTIONS ON TERMINATE SIGNAL CALL tb_insrt
    
    MENU
        COMMAND "RECREATE TABLE"
               WHENEVER ANY ERROR CONTINUE
                 DROP TABLE cl_term
             WHENEVER ANY ERROR STOP 
             CREATE TABLE cl_term(
                 f_int INTEGER 
                 )
          COMMAND "OPEN EXCEPTION"
            OPEN WINDOW w1 WITH FORM "testform"
          COMMAND "CHECK TABLE REC"
            SELECT COUNT(*) INTO cnt FROM cl_term
            DISPLAY cnt
        COMMAND "EXIT"
            EXIT MENU    
    END MENU
END MAIN

FUNCTION tb_insrt()
    INSERT INTO cl_term VALUES ("1")
END FUNCTION

Following is the instruction on how to utilize the above program:

1. Set the correct DATABASE in 4gl
2. Compile and run the program
3. Click "RECREATE TABLE"
4. Click "CHECK TABLE REC" (to make sure that the table is empty. Once you close the browser tab/window, the table will be populated with one row of data)
5. Close the browser tab/window, this event will trigger ON TERMINATE to call the tb_insrt() function which will populate the table with one row of data (Note: error, such as the OPEN EXCEPTION also triggers ON TERMINATE option)
6. Run the program again and click "CHECK TABLE REC" button. It shows you count of inserted rows into the table