export class TimeStampService {  private _localTimestamp: number;   // 本地时间戳  private _serveTimestamp: number;  // 服务器端时间戳  private _duration: number = 1000 * 60 * 5; // 时间戳更新频率 （毫秒)  private _timeDiffer: number; // 服务器和本地的时间差 服务器-本地  constructor(  ) {    this._timeDiffer = 0;    this.getTimeDiffer();  }  private getTimeDiffer() {    const xhr = new XMLHttpRequest();    xhr.open('get', environment.URL_TIME, true);    const that = this;    xhr.onload = function () {      if (this.status === 200) {        const result = JSON.parse(this.response);        const now = new Date().getTime();        that._timeDiffer = result.data.timestamp - now;      }    };    xhr.onerror = function () {      console.log('xhr error', xhr);    };    xhr.send();  }  get Duration() {    return this._duration;  }  get ServerTimeStamp() {    if (!this._localTimestamp) {      this._localTimestamp = new Date().getTime();    } else {      const now = new Date().getTime();      // 提前30秒做一次异步矫正      if (now - this._localTimestamp > this.Duration - 1000 * 30) {        this.getTimeDiffer();  // 更新差值 防止用户修改本地时间      }      if (now - this._localTimestamp > this.Duration) {        this._localTimestamp = now;      }    }    this._serveTimestamp = this._localTimestamp + this._timeDiffer;    return this._serveTimestamp;  }}

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