The Complete Guide to LWC Lifecycle Hooks

If you want to move beyond basic “Hello World” components and build robust, professional Salesforce applications, you have to understand the LWC Lifecycle.

In this tutorial we’ll go over every single lifecycle hook available in Lightning Web Components. These hooks allow you to intervene at specific moments—like when a component loads, renders, or leaves the screen—to fetch data, manipulate the UI, or clean up garbage.

Below is a comprehensive guide to what they are, when to use them, and the common traps to avoid.

The Lifecycle Flow

(Video: [03:20])

Before diving into specific hooks, it is critical to understand the order of operations, especially when you have a Parent component containing Child components. The flow isn’t always intuitive:

Parent Constructor fires.
Parent is inserted into the DOM.
Parent ConnectedCallback fires.
Parent Render begins.
Child Constructor fires.
Child ConnectedCallback fires.
Child RenderedCallback fires.
Parent RenderedCallback fires (Last!).

Notice that the Parent’s RenderedCallback only happens after all its children have finished rendering. This is crucial for timing your logic correctly.

1. Constructor()

(Video: [12:26])

The constructor() is the very first thing that runs. However, it is also the most limited.

The Constraint: You cannot access public properties (@api variables) or Child components here. If you try to access this.recordId, it will be undefined.
Best Use Case: Use this for tasks that don’t require Salesforce data, such as initializing simple variables or prepping data structures that don’t rely on the DOM.

2. ConnectedCallback()

(Video: [15:17])

This is arguably the most used hook in LWC development. It runs when the component is inserted into the DOM.

Why it’s great: Public properties (like @api recordId) are now available.
Best Use Cases:
- Fetching data from Apex.
- Setting up event listeners (e.g., subscribing to Lightning Message Service).
- Initializing local storage caches.
Warning: It can be called multiple times if the component is removed and re-added to the DOM (e.g., in a dynamic multi-page wizard).

3. RenderedCallback()

(Video: [24:59])

This hook runs after the component (and its children) has finished rendering.

The Capability: This is the first time you can access and manipulate Child components.
The Danger Zone: This hook fires often. Every time a reactive property used in your HTML changes, renderedCallback runs again.
The Trap: If you update a reactive property inside renderedCallback, you can trigger an infinite loop (Update -> Re-render -> Update -> Re-render). Always use a “guard clause” (e.g., if(!this.hasLoaded)) to ensure your logic only runs once.

4. Render() Method

(Video: [30:50])

While not technically a “hook,” the render() method allows you to override the default HTML template.

Best Use Case: Dynamic Templates. For example, if you want to render a specific layout for Mobile users and a completely different layout for Desktop users, you can import two separate HTML files and return the correct one inside this method based on your logic.

5. DisconnectedCallback()

(Video: [39:49])

This hook runs when your component is removed from the DOM. It is the “janitor” of the lifecycle.

Why you need it: If you set up event listeners or stored data in the browser’s cache during connectedCallback, they don’t automatically disappear when the component closes.
Best Use Case: Cleaning up! Use this to unsubscribe from message channels, remove event listeners, and clear local storage to prevent memory leaks or weird bugs.

6. ErrorCallback()

(Video: [42:46])

Think of this as a try/catch block for your UI.

How it works: If a Child component crashes or throws an error, this hook in the Parent component can catch it.
Best Use Case: Instead of showing the user a white screen or a raw error log, use this hook to display a friendly “Something went wrong” toast notification or a custom error UI.

For the full deep dive and code examples, watch the original video here: https://youtu.be/Kc4xtTKbLMM

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Salesforce Development Books I Recommend

Advanced Apex Programming
Salesforce Lightning Platform Enterprise Architecture
Mastering Salesforce DevOps

Good Non-SF Specific Development Books:

Clean Code
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AI DISCLAIMER: Gemini assisted me in writing this blog post by analyzing and summarizing the contents on the YouTube video I created that is linked at the top of this post.