Global event system for React.js

EventSystem.js

class EventSystem {
    constructor() {
        this.queue = {};
    }

    publish(event, data) {
        let queue = this.queue[event];

        if (typeof queue === 'undefined') {
            return false;
        }

        while (queue.length > 0) {
            (queue.shift())(data);
        }

        return true;
    }

    subscribe(event, callback) {
        if (typeof this.queue[event] === 'undefined') {
            this.queue[event] = [];
        }

        this.queue[event].push(callback);
    }

    //  the callback parameter is optional. Without it the whole event will be removed, instead of
    // just one subscibtion. Enough for simple implementations
    unsubscribe(event, callback) {
        let queue = this.queue;

        if (typeof queue[event] !== 'undefined') {
            if (typeof callback === 'undefined') {
                delete queue[event];
            } else {
                this.queue[event] = queue[event].filter(function(sub) {
                    return sub !== callback;
                })
            }
        }
    }
}

module.exports = new EventSystem();

sample-usage-to-publish.js

var RiskList = React.createClass({
  getInitialState: function() {
    return { risks: [] };
  },
  componentDidMount: function() {
    // someting
  },
  render: function() {
    EventSystem.publish('risk.count.update', this.state.risks.length);
    // something
  }
}

sample-usage-to-subscribe.js

var RiskPage = React.createClass({
  updateRiskCount: function(count) {
    this.setState({
      riskCount: count
    });
  },
  componentDidMount: function() {
    EventSystem.subscribe('risk.count.update', this.updateRiskCount);
  },
  componentWillMount: function() {
    EventSystem.unsubscribe('risk.count.update', this.updateRiskCount);
    // Removes all subscriptions to this event. Would do same and simpler for this example
    // EventSystem.unsubscribe('risk.count.update', this.updateRiskCount);
  },
  getInitialState: function() {
    return {
      riskCount: 0
    };
  },
  render: function() {
    // something
  }
});