Application Events in Salesforce Lightning Framework

Lightning framework is based on event-driven architecture which allows to communicate between different events. Lightning events are fired from JavaScript controller actions that are triggered by a user interacting with the user interface.

The communication between components are handled by events. There are two types of custom events in the Lightning Framework:

  • Component Events
  • Application Events

Application Events are handled by any component have handler defined for event.These events are essentially a traditional publish-subscribe model.

Application Event Example:
In below example by using Application event, I’m passing the values from Component1 to a Component2 via event.

Sample Application Event:
Create a sample application type event. Use type=”APPLICATION” in the aura:event tag for an application event. The attribute type is the one that will differentiate Application event from Component event.

<aura:event type="Application" description="Sample Application Event">
    <aura:attribute name="message" type="String" />


    <aura:registerEvent name="SampleApplicationEvent" type="c:SampleApplicationEvent"/>
    <lightning:button label="Click to fire the event" variant="brand" onclick="{!c.component1Event}"/>

Component1 JS Controller:
Use $A.get(“e.myNamespace:myAppEvent”) in JavaScript to get an instance of the myAppEvent event in the myNamespace namespace.
To set the attribute values of event, call event.setParam() or event.setParams().

    component1Event : function(cmp, event,helper) { 
        //Get the event using event name. 
        var appEvent = $A.get("e.c:SampleApplicationEvent"); 
        //Set event attribute value
        appEvent.setParams({"message" : "Welcome "});; 

The application event handled by the Component2 that fired using aura:handler in the markup.
The action attribute of aura:handler sets the client-side controller action to handle the event.

    <aura:attribute name="eventMessage" type="String"/> 
    <aura:handler event="c:SampleApplicationEvent" action="{!c.component2Event}"/>
    <div class="slds-m-around_xx-large">

Component2 JS Controller:

    component2Event : function(cmp, event) { 
        //Get the event message attribute
        var message = event.getParam("message"); 
        //Set the handler attributes based on event data 
        cmp.set("v.eventMessage", message + 'Biswajeet');         

Lightning Application:

<aura:application extends="force:slds">