How to make a pop-up tip automatically close in 2 seconds

I want the “alert(”Existing table header“);” to disappear automatically in 2 seconds!
I found a code from the internet and it doesn't seem right.

  $(document).ready(function() {
        // Show warning box
        $("#alert-box").fadeIn(500, function() {
            // Automatically turns off after a certain period of time (e.g. 3 seconds)
            setTimeout(function() {
                $("#alert-box").fadeOut(500);
            }, 3000); // 3000 milliseconds = 3 seconds
        });
    });

My original code.

var cell = app.activeDocument.selection[0].parent;
var myTable = cell.parent;

firstRow = myTable.rows[0];
//add 1 row at the table top
if ((firstRow.rowType !== RowTypes.HEADER_ROW) && (myTable.rows[0].cells[0].contents !==contName))
    {
    dupeTopRow(myTable);
    myTable.rows.add(LocationOptions.BEFORE, myTable.rows[0]);
/**
* duplicate the first row af a myTable
* @ param the myTable
* @ return void
*/
function dupeTopRow(t){
    var newRow = t.rows.add(LocationOptions.BEFORE, t.rows[0]);
    var newCell = newRow.cells
    var lr = t.rows[1].cells
    for (var i = 0; i < newCell.length; i++){
        newCell[i].properties = lr[i].properties;
    };  
}
}
else{
alert("Existing table header ")
exit ();
}

 Thnak you very much.