一、关键代码：

<el-date-picker 
v-model="form.time" 
type="daterange" 
value-format="yyyy-MM-dd" 
range-separator="至"
start-placeholder="开始日期" 
end-placeholder="结束日期">
 </el-date-picker>

// 默认设置最近3天
this.form.time = [
	formatDate(new Date().setHours(0, 0, 0, 0) - 3600 * 1000 * 24 * 3), 
	formatDate(new Date().setHours(0, 0, 0, 0) )
]

formatDate(time) {
       const fnW = str => {
           var num;
           str >= 10 ? (num = "" + str) : (num = "0" + str);
           return num;
       };
       const dt = new Date(time);
       const y = dt.getFullYear().toString();
       const mt = dt.getMonth() + 1;
       const day = dt.getDate();
       const h = dt.getHours();
       const m = dt.getMinutes();
       const s = dt.getSeconds();
       // 年月日字符串
       return y + '-' + fnW(mt) + '-' + fnW(day);
}