js倒計(jì)時(shí)同步

js倒計(jì)時(shí)同步問題 當(dāng)我兩個(gè)用戶同步打開這個(gè)頁面的時(shí)間，他們的倒計(jì)時(shí)時(shí)間會(huì)相差幾秒鐘，
PS：我應(yīng)該怎么寫這個(gè)倒計(jì)時(shí)
PS：我這寫法有問題嗎？

      let expires_at = new Date(this.order.expires_at.replace(/-/g, '/'));  // 結(jié)束時(shí)間
      let myDate = new Date()//獲取當(dāng)前的時(shí)間毫秒
      let ms = expires_at-myDate   //轉(zhuǎn)化的毫秒
      let mm = parseInt(ms/60000)//轉(zhuǎn)換成分鐘
      let mss = ms%60          //毫秒取余數(shù)
      this.minutes = mm
      this.seconds =  mss
      a()
      
   function a(){   
     setInterval(()=>{
           if (this.seconds == 0 && this.minutes != 0) {
          this.seconds = 59;
          this.minutes -= 1;
        }else if(this.minutes == 0 && this.seconds == 0){
          this.seconds = 0;
        
          clearInterval();

        }else{
          this.seconds -= 1
        }
      },1000);
      }