EmpApiDemo.xml

<aura:component access="global">
    <!-- ChannelName, which needs to subscribed -->
    <aura:attribute name="channelName" type="String" required="true"/>
    <!-- Save the reference of current subscription, which can be unsubscribe later on -->
    <aura:attribute name="subscription" type="Object"/>
     
    
    <!-- This event is fired when a component is destroyed. 
		Handle this event if you need to do custom cleanup when a component is destroyed.-->
    <aura:handler name="destroy" value="{!this}" action="{!c.unsubscribe}"/>
	<!-- init event -->
    <aura:handler name="init" value="{!this}" action="{!c.subscribe}"/>
    
    <!-- empApi component which will be used to subscribe/unsubscribe to a channel -->
    <lightning:empApi aura:id="empApi"/>
    
    <!-- Component event, which will be fired once the message is received
         This event will be handled by parent component to perform needful action on stream event -->
    <aura:registerEvent name="onEmpEvent" type="c:EmpEvent"/>
</aura:component>