Lightning Aura Components Developer Guide

What Is the Lightning Component Framework?
Quick Start
Creating Components
Using Components
Communicating with Events
Communicating Across the DOM with Lightning Message Service
Creating Apps
Styling Apps
Developing Secure Code
Using JavaScript
Supported JavaScript
Invoking Actions on Component Initialization
Sharing JavaScript Code in a Component Bundle
Sharing JavaScript Code Across Components
Using External JavaScript Libraries
Dynamically Creating Components
Detecting Data Changes with Change Handlers
Finding Components by ID
Working with Attribute Values in JavaScript
Working with a Component Body in JavaScript
Working with Events in JavaScript
Modifying the DOM
Checking Component Validity
Modifying Components Outside the Framework Lifecycle
Throwing and Handling Errors
Calling Component Methods
Dynamically Adding Event Handlers To a Component
Dynamically Showing or Hiding Markup
Adding and Removing Styles
Which Button Was Pressed?
Formatting Dates in JavaScript
Using JavaScript Promises
Making API Calls from Components
Create CSP Trusted Sites to Access Third-Party APIs
Working with Salesforce Data
Testing Components with Lightning Testing Service
Debugging
Performance
Reference
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Invoking Actions on Component Initialization

Use the init event to initialize a component or fire an event after component construction but before rendering.

The init event is fired only once per lifecycle of the component. The init event doesn’t get fired if the component is served from cache. To execute JavaScript code every time a component is rendered, use the render event instead.

Note

Let’s look at an example.

The magic happens in this line.

This code registers an init event handler for the component. init is a predefined event sent to every component. Setting value="{!this}" marks this as a value event. You should always use this setting for an init event.

After the component is initialized, the doInit action is called in the component’s controller.

The doInit action sets an attribute value, but it could do something more interesting, such as firing an event.

If a component is contained in another component or app, the inner component is initialized first.