How can we subscribe to an event in Salesforce Lightning Component?

In order to use Application event we need to follow the Four simple steps

1. Create Application Event
2. Fire the event from the child component
3. handle the event into Parent Component
4. Execute the action into Parent Component

Step 1 – Create Application Event

Open developer console and then File -> New -> Lightning Event -> name it applicationEvent and use below code.

<aura:event type=”APPLICATION” description=”Event template” >
<aura:attribute name=”testWord” type=”String” />
</aura:event>

Step 2 – Register the event

Unlike the Component we do not need to register the Application Event.

Step 3 – Fire the component Event

Use below code in javascript to execute the event.

({
handleClick : function(component, event, helper) {
var appEvent = $A.get(‘e.c:applicationEvent’);
appEvent.setParams({
“testWord” : ‘Value From Application Event’
});
appEvent.fire();
},
})

Explanation : –

$A.get(‘e.c:applicationEvent’); – Finds the event with the name provided after c: and in our case it it applicationEvent.
setParams : – is used to send the parameters to the parent component if we are using any attribute in the event. In our case we have used attribute testWord
fire() :- Executes the event

Step 4: – Handle the Event in any Component

A single line of code to handle the event into the component

<aura:handler event=”c:applicationEvent” action=”{!c.doHandleCompEvent}” />