            $(document).ready(function() {
                var numDigits = 10;
                var timeDelay = numDigits * 1000;

                function createDropdowns() {
                    var digitDropdown = $("<select>").change(function() {
                        numDigits = $(this).val();
                    });

                    var timeDropdown = $("<select>").change(function() {
                        timeDelay = $(this).val();
                    });

                    for (var i = 2; i <= 20; i += 2) {
                        if (i == numDigits) {
                            timeDropdown.append($("<option>").attr("value", i * 1000).attr("selected", "selected").append(i * 1000));
                            digitDropdown.append($("<option>").attr("value", i).attr("selected", "selected").append(i));
                        } else {
                            timeDropdown.append($("<option>").attr("value", i * 1000).append(i * 1000));
                            digitDropdown.append($("<option>").attr("value", i).append(i));
                        }
                    }

                    $("#dropdowns").append($("<span>").append("Number of digits  ").append(digitDropdown).append("<br>").append("<br>")).append($("<span>").append("Time delay ").append(timeDropdown).append("<br>").append("<br>"));

                    var button = $("<button>").attr("id", "butt").html("Go");
                    button.click(function() {
                        var classCheck = $("tr#row2").hasClass("invisible");
                        if (classCheck) {
                            $("#table").removeClass("invisible");
                            $("tr#row2").removeClass("invisible");
                            $(this).html("Go!");
                        } else {
                            generate();
                            $(this).html("Reveal");
                        }
                    });

                    $("#makeItSo").append(button);
                }

                function generate() {
                    var mainTable = $("<table>").attr("id", "table");
                    var mainTableRow1 = $("<tr>").attr("id", "row1");
                    for (var i = 1; i <= numDigits; i++) {
                        mainTableRow1.append($("<td>").attr("id", "dg" + i).append(Math.floor(Math.random() * 1000 % 10)));
                    }
                    var mainTableRow2 = $("<tr>").attr("id", "row2").addClass("invisible");
                    for (i = 2; i <= numDigits; i += 2) {
                        mainTableRow2.append($("<td>").attr("id", "peg" + i).attr("colspan", 2).append("xxx"));
                    }
                    mainTable.append(mainTableRow1).append(mainTableRow2);
                    $("#main").html("").append(mainTable);

                    $("#butt").addClass("invisible");
                    setTimeout(function() {
                        $("#butt").removeClass("invisible");
                        mainTable.addClass("invisible");
                    }, timeDelay);
                }

                createDropdowns();

            });

Setting Validate Copy Format

.invisible {
  display: none;
}

Setting Validate Copy Format