Ember Master Tab

Synopsis

This addon provides a service that allows you to run code on a single tab of your ember application. You might find this useful if your app has functionality that for some reason does not make sense or it is wasteful/redundant to have it run on every tab that is currently open. For example, you might be continuously pulling some state from your server API that you are saving on localStorage which you then use to update your UI through event listeners.

Compatibility

• Ember.js v3.12 or above
• Ember CLI v2.13 or above
• Node.js v10 or above

Notes

• The service ensures that only one master tab exists at any one time.
• If the current master tab closes or refreshes, any other tab can take the responsability at that time.
• If the current master tab crashes, currently no other tab will take the responsability until a new tab is opened.
• This service is most useful on objects that provide global functionality to your application, such as other services.

ember install ember-master-tab

Code Example

You can clone this repository and have a look at the dummy app to see it in action.

run(func1, options = {}).else(func2)

• func1: If this is the master tab, run this function.
• options (optional):
• force (optional, default: false): If true, run func1 irregardless of this being the master tab or not.
• func2: If this is not the master tab, run this instead.

// services/server-time-run.js
import Ember from 'ember';

export default Ember.Service.extend({
  masterTab: Ember.inject.service(),
  currentTime: null,
  init() {
    this._super(...arguments);
    window.addEventListener('storage', e => { // only slave tabs will receive this event
      if (e.key === 'current-time-run') {
        this.set('currentTime', e.newValue);
      }
    });
    this._updateTime();
  },
  _updateTime() {
    Ember.run.later(() => {
      this.updateTime();
      this._updateTime();
    }, 900);
  },
  updateTime(force = false) {
    this.get('masterTab')
      .run(() => {
        Ember.$.getJSON('/api/current-time').then(data => { // will only run on the master tab
          const currentTime = data.currentTime;
          this.set('currentTime', currentTime);
          localStorage['current-time-run'] = currentTime;
        });
      }, { force })
      .else(() => {
        // Master tab is handling it.
      });
  }
});

Notes:

• else() is optional.
• run() takes a second optional boolean parameter. If true it will make the function run irregardless of this being the master tab or not for that call on that tab and the function passed to else() will not run. Considering the previous example, this would be useful if a controller calls this.get('serverTimeRun').updateTime(true) directly on any tab.

lock(lockName, func1, options = {}).wait(func2)

• lockName: Name of the lock.
• func1: Function which returns a Promise that will run only if this is the master tab. Once the promise resolves or rejects, the lock will be freed.
• options (optional):
• force (optional, default: false): If true, run func1 irregardless of this being the master tab or not.
• waitNext (optional, default: true): If true and there is currently no lock present, wait a maximum of waitNextDelay until the lock has been obtained and released.
• waitNextDelay (optional, default: 1000): If waitNext is true, wait this amount of milliseconds.
• func2: If this is not the master tab, run this instead once the lock has been freed.

// services/server-time-lock.js
import Ember from 'ember';

export default Ember.Service.extend({
  masterTab: Ember.inject.service(),
  currentTime: null,
  init() {
    this._super(...arguments);
    this._updateTime();
  },
  _updateTime() {
    Ember.run.later(() => {
      this.updateTime();
      this._updateTime();
    }, 900);
  },
  updateTime(force = false) {
    this.get('masterTab')
      .lock('server-time', () => {
        return Ember.$.getJSON('/api/current-time').then(data => { // will only run on the master tab
          const currentTime = data.currentTime;
          this.set('currentTime', currentTime);
          return currentTime; // will be passed to slave tabs
        });
      }, { force })
      .wait(currentTime => { // will only run on slave tabs; currentTime is the result from the master tab
        this.set('currentTime', currentTime);
      });
  }
});

Notes:

• wait() is optional. It can take a second callback which runs if the promise failed.
• If the master tab is currently running the promise (there is a lock present), the callbacks passed to wait() will execute once that promise resolves/rejects. Otherwise, they will run immediately. These callbacks only run on "slave" tabs, generally.
• You use this if you need "slave" tabs to wait for whatever the master tab's promise returns. Maybe your service defers readiness of the application's initialization and you need the master tab to finish loading giving slave tabs its state.
• The value passed to the wait() callbacks will be the last value returned by the lock() promise.
• If options.force is true it will make the function run irregardless of this being the master tab or not for that call on that tab. It sets a lock and the callbacks passed to wait() will not run. If the master tab encounters a lock during this, it will instead run the wait() callbacks. Considering the previous example, this would be useful if a controller calls this.get('serverTimeLock').updateTime(true) directly on any tab.
• The service will save to localStorage whatever the promise returns. This value will be passed to the appropriate callback given to wait(). Note that localStorage only stores strings. So make sure whatever your promise returns can easily be converted to something usable in your wait() callbacks.

isMasterTab event

Whenever a tab is promoted to master status, the masterTab service will emit an isMasterTab event. So, following the theme of the previous examples, you could also work with EventSource objects (or WebSocket, etc.) like this:

// services/server-time-sse.js
import Ember from 'ember';

export default Ember.Service.extend({
  masterTab: Ember.inject.service(),
  currentTime: null,
  init() {
    this._super(...arguments);
    if (this.get('masterTab.isMasterTab')) {
      this.setup();
    }
    this.get('masterTab').on('isMasterTab', isMaster => {
      if (isMaster) {
        this.setup();
      }
    });
    window.addEventListener('storage', e => {
      if (e.key === 'current-time-sse') {
        this.set('currentTime', e.newValue);
      }
    });
  },
  setup() {
    const sse = new EventSource('/sse');
    sse.onmessage = e => {
      this.set('currentTime', e.data);
      window.localStorage['current-time-sse'] = e.data;
    };
    this.get('masterTab').on('isMasterTab', isMaster => {
      if (!isMaster) {
        sse.close();
      }
    });
  }
});

Notes:

• The event is only raised after the application has been initialized. Therefore, the master tab will not emit it. It will only be triggered if the master tab is closed/refreshed and a different tab is promoted.

License

Ember Master Tab is released under the MIT Licencse.