code: function getMonthDays(timestamp = Date.now()) {
    const cursorDay = new Date(new Date(timestamp).setDate(1));
    const currentMonth = cursorDay.getMonth();
    const days = [];
    while (cursorDay.getMonth() === currentMonth) {
      days.push(cursorDay.getTime());
      cursorDay.setDate(cursorDay.getDate() + 1);
    }
    return days;
  }
docs: /*
  根据 timestamp 去计算它所属的月份的全部 days
  days数据结构为：[timestamp1, timestamp2, ...]