formatChatTime(dateTimeStr) {
      if (!dateTimeStr) {
        return "";
      }
      var dateTime = new Date(dateTimeStr);
      let year = dateTime.getFullYear();
      let month = this.formatDigit(dateTime.getMonth() + 1);
      let date = this.formatDigit(dateTime.getDate());
      let hour = this.formatDigit(dateTime.getHours());
      let minute = this.formatDigit(dateTime.getMinutes());
      let second = this.formatDigit(dateTime.getSeconds());

      return `${year}/${month}/${date} ${hour}:${minute}:${second}`;
    },
    formatDigit(digit) {
      return digit > 9 ? digit : "0" + digit;
    },