js中获取某个月份的第一天和最后一天的日期，返回年-月-日格式

js中获取某个月份的第一天和最后一天的日期，返回年-月-日格式

<script type="application/javascript">

    // 显示2023-3-01,2023-3-31
    document.write(getDay(2023,3));


    function getDay(year, month) {
    
    
            var firstDay = new Date(year, month - 1, 1); //这个月的第一天
            var currentMonth = firstDay.getMonth(); //取得月份数
            var lastDay = new Date(firstDay.getFullYear(), currentMonth + 1, 0); //是0而不是-1

            var fy = firstDay.getFullYear(); //获取年份
            var fm = firstDay.getMonth() + 1; //获取月份
            firstDay = [fy, fm, '01'].join("-");


            var ly = lastDay.getFullYear(); //获取年份
            var lm = lastDay.getMonth() + 1; //获取月份
            var ld = lastDay.getDate();
            lastDay = [ly,lm, ld].join("-");

            return [firstDay, lastDay];
    }

</script>