1.页面

<template>
  <div>
    <div>
      <!-- 当前日期 -->
      <p>{{ aa }}</p>  
      <!-- 七天前日期     -->
      <p>{{ bb }}</p>
      <!-- 当前星期日期 -->
      <p>{{ nowWeek }}</p>
    </div>
  </div>
</template>

2.在data和created定义方法

data() {
    return {
      nowWeek: "",
      aa: "",
      bb:"",
    };
  },
  created() {
    this.timer = setInterval(() => {
      this.getTime(0);
      this.aa = this.getTime(0);
      this.bb = this.getTime(7);
    }, 1000);
  },

2.在methods里写方法

methods: {
    getTime(val) {
      //   获取时间并格式化
      var now = new Date();
      val === 0 ? "" : now.setTime(now.getTime() - 24 * 60 * 60 * 1000 * val); //   获取前val天的时间
     // val === 0 ? "" : now.setTime(now.getTime() + 24 * 60 * 60 * 1000 * val); //   获取后val天的时间
      const y = now.getFullYear();
      const m = (now.getMonth() + 1 + "").padStart(2, "0");
      const d = (now.getDate() + "").padStart(2, "0");
      const hh = (now.getHours() + "").padStart(2, "0");
      const mm = (now.getMinutes() + "").padStart(2, "0");
      const ss = (now.getSeconds() + "").padStart(2, "0");
      //获取当前的星期
      let wk = now.getDay();
      let weeks = [
        "星期日",
        "星期一",
        "星期二",
        "星期三",
        "星期四",
        "星期五",
        "星期六",
      ];
      let week = weeks[wk];
      this.nowWeek = week;
      return `${y}-${m}-${d} ${hh}:${mm}:${ss}`; // 获取的时间格式为 2021-11-16 11:37:15
      //return `${y}年${m}月${d}日 ${hh}:${mm}:${ss}`; // 获取的时间格式为 2021年11月16日 11:37:15
      // return `${y}-${m}-${d} ${hh}:${mm}:${ss}`; // 获取的时间格式为 2021-04-09 11:37:15
      // return y + m + d                           // 获取的时间格式为  20210409
    },
  },