Vue plugin to retrieve the server time

server-time.vue

//+ Jonas Raoni Soares Silva
//@ http://raoni.org

export default class ServerTime {
  constructor ({http = new Error('http parameter is required'), url = new Error('url is required'), thresholdDelay = 300, autoSynchronizeProbes = 0}) {
    Object.assign(this, {
      http,
      url,
      thresholdDelay,
      best: null
    });
    for (let promise = Promise.resolve(), i = autoSynchronizeProbes; i-- > 0;) {
      promise = promise.then(() => this.synchronize()).catch(error => {
        console.error(error);
      });
    }
  }

  synchronize () {
    return new Promise(resolve => {
      const start = +new Date();
      return this.http.get(this.url).then(response => {
        const now = +new Date();
        const requestDelay = now - start;
        if (!this.best || requestDelay < this.best.requestDelay) {
          this.best = {
            requestDelay,
            delay: now - (requestDelay >> 1) - (+new Date(response.body) || +new Date(response.headers.get('Date')))
          };
          resolve(this);
        }
      });
    });
  }

  getDate () {
    if (!this.best || this.best.requestDelay > this.thresholdDelay) {
      this.synchronize().catch(error => {
        console.error(error);
      });
    }
    return new Date(+new Date() - (this.best ? this.best.delay : 0));
  }

  toString () {
    return this.getDate() + '';
  }

  valueOf () {
    return +this.getDate();
  }

  [Symbol.toPrimitive] (hint) {
    return hint === 'number' ? this.valueOf() : this.toString();
  }

  static install (Vue, options) {
    Vue.prototype.$serverTime = new ServerTime(options);
  }
}