前端传月份自动识别月初，月末

let  startTime = '2020-01-01'

let endTime = '2020-08-01'

let date = endTimeIf(startTime .substr(0, 4), startTime .substr(5,2))

// year 年份 value月份 返回当前月的最后一天

function endTimeIf(year, value) {

let t = ['02']

let t1 = [ '04', '06', '09', '11']

let t2 = ['01', '03', '05', '07', '08', '10', '12']

if (t.indexOf(value) !== -1) {

if (Number(year) /4 ===0) {

return '29'

    }else {

return '28'

    }

}

if (t1.indexOf(value) !== -1) {

return '30'

  }

if (t2.indexOf(value) !== -1) {

return '31'

  }

}