<el-date-picker
    v-model="value1"
    type="date"
    value-format="yyyy-MM-dd"
    placeholder="選擇日期"
    size="small"
    @change="getTimeRange"
  >
  </el-date-picker>

JS方法

getTimeRange (value) {
  let date = new Date(value); //value的格式為YYYY-MM-DD
  let month = (date.getMonth() + 1).toString().padStart(2,'0'); //獲取月份，如果月份小于10加個(gè)‘0’
  let year = date.getFullYear();
  this.startTime = year + '' + month + '01';
  let day = new Date(year,month,0);
  this.endTime = year + '' + month + '' + day.getDate();
},