为什么包括.appendChild（）的第一条指令未执行

Question

当我显示一个日历都可以正常工作时，我正在使用javascript制作日历，但是当我想在我的网页上显示两个日历时，似乎没有执行appendChild（）函数之一

function showCalendar(month, year) {

    let firstDay = (new Date(year, month)).getDay();

    tbl = document.getElementById("calendar-body");
    tb2 = document.getElementById("calendar-body2");// body of the calendar

    // clearing all previous cells
    tbl.innerHTML = "";
    tb2.innerHTML = "";

    // filing data about month and in the page via DOM.
    monthAndYear.innerHTML = months[month] + " " + year;
    monthAndYear2.innerHTML = months[month] + " " + year;
    selectYear.value = year;
    selectYear2.value = year;
    selectMonth.value = month;
    selectMonth2.value = month;

    // creating all cells
    let date = 1;
    for (let i = 0; i < 6; i++) {
        // creates a table row
        let row = document.createElement("tr");

        //creating individual cells, filing them up with data.
        for (let j = 0; j < 7; j++) {
            if (i === 0 && j < firstDay) {
                cell = document.createElement("td");
                cellText = document.createTextNode("");
                cell.appendChild(cellText);
                row.appendChild(cell);
            }
            else if (date > daysInMonth(month, year)) {
                break;
            }

            else {
                cell = document.createElement("td");
                cellText = document.createTextNode(date);
                if (((date === today.getDate())||(date === (today.getDate()-1))||(date === (today.getDate()-2))) && year === today.getFullYear() && month === today.getMonth()) {
                    cell.classList.add("bg-info");

                } // color today's date
                cell.appendChild(cellText);
                row.appendChild(cell);
                date++;
            }


        }

        tbl.appendChild(row);
        tb2.appendChild(row);
        // appending each row into calendar body.
    }

}


tbl.appendChild(row);
tb2.appendChild(row);

当我切换这两条指令时，第二条指令有效，但第一条指令无效