fullcalendar 点击prev获取月份第一天

fullcalendar 点击上一页/下一页获取当前页的月份第一天

import dayjs from 'dayjs'
// ...
        currentDate = this.calendarApi.getDate()
        beginTime = dayjs(currentDate).startOf('month').toDate()
        endTime = dayjs(currentDate).endOf('month').toDate()