// Client-side function that invokes the subscribe method on the empApi component.
subscribe: function (component, event, helper) {
    // Get the empApi component.
    console.log('calling to subscribe');
    debugger;
    var empApi = component.find('empApi');
    // Get the channel from the attribute.
    var channel = component.get('v.channel');
    // Subscription option to get only new events.
    var replayId = -1;
    // Callback function to be passed in the subscribe call.
    // After an event is received, this callback prints the event
    // payload to the console. A helper method displays the message
    // in the console app.
    var subscribeCallback = function (message) {
        console.log('Event Received : ' + JSON.stringify(message));
        helper.onReceiveNotification(component, message);
    };
    // Subscribe to the channel and save the returned subscription object.
    empApi.subscribe(channel, replayId, subscribeCallback).then($A.getCallback(function (newSubscription) {
        console.log('Subscribed to channel ' + channel);
        component.set('v.subscription', newSubscription);
    }));

    /*.catch(
        function(error) {
            console.error('cant subscribe to event ', JSON.stringify(error));
        }
    );*/
},

empApi.subscribe(channel, replayId, subscribeCallback).then($A.getCallback(function (newSubscription) {
    console.log('Subscribed to channel ' + channel);
    component.set('v.subscription', newSubscription);
}));