Ligthning - Passing data up and around the component hierarchy via an application component

applicationEvent.evt

<aura:event type="APPLICATION">
  <aura:attribute name="param" type="String"/>
</aura:event>

applicationEventReceiver.cmp

<aura:component>
	<aura:handler event="c:applicationEvent" action="{!c.handleMyApplicationEvent}"/>
</aura:component>

applicationEventReceiverController.js

({
    handleMyApplicationEvent : function(component, event, helper) {
        var value = event.getParam("param");
        alert("Received application event with param = "+ value);
    }
})

applicationEventSender.cmp

<aura:component>
	<aura:registerEvent name="myApplicationEvent" type="c:applicationEvent"/>
    
  <lightning:button label="Fire application event" onclick="{! c.fireMyApplicationEvent }" />
</aura:component>

applicationEventSenderController

({
    fireMyApplicationEvent : function(component, event, helper) {
        var myEvent = $A.get("e.c:applicationEvent");
        myEvent.setParams({"param": "It works!"});
        myEvent.fire();
    }
})