Lightning Web Components (LWC) power modern Salesforce applications with lightning-fast UI and modular design. But here’s the secret sauce 👇 — understanding Lifecycle Hooks is what separates a basic component from a production-ready one.
Lifecycle hooks let you control what happens when a component is created, rendered, updated, and destroyed. If you know when to use which hook, you’ll avoid bugs, reduce performance issues, and write clean, scalable code.
🚀 LWC Lifecycle Stages (Quick Recap)
- Creation – Component is born, constructor runs.
- Render – Template is rendered.
- Re-render – Updates after reactive property changes.
- Destruction – Component is removed from DOM.
🔑 Lifecycle Hooks in Action
1️⃣ constructor()
– Initialization
📍 When it runs: When component is created, before it hits the DOM.
💡 Use Case: Initialize default values. Avoid DOM access here.
constructor() {
super();
this.filterCriteria = 'Active Students';
}
✅ Great for setting internal state, NOT for fetching data.
2️⃣ connectedCallback()
– DOM Entry Point
📍 When it runs: When component is inserted into the DOM.
💡 Use Case: Fetch data, call Apex, subscribe to events.
connectedCallback() {
getStudents()
.then(result => {
this.students = result;
})
.catch(error => {
this.error = error;
});
}
✅ Perfect for Apex calls, pub-sub setup, listeners.
3️⃣ renderedCallback()
– After Every Render
📍 When it runs: Every time DOM is rendered.
💡 Use Case: DOM manipulations, scroll handling, third-party library init.
renderedCallback() {
if (!this.isRendered) {
this.template.querySelector('lightning-input').focus();
this.isRendered = true;
}
}
⚠️ Use carefully — avoid infinite loops.
4️⃣ disconnectedCallback()
– Cleanup Time
📍 When it runs: When component is removed from DOM.
💡 Use Case: Unsubscribe, clear intervals, disconnect observers.
disconnectedCallback() {
unsubscribe(this.subscription);
this.subscription = null;
}
✅ Prevents memory leaks.
5️⃣ errorCallback(error, stack)
– Error Handling
📍 When it runs: If error occurs in lifecycle methods or child components.
💡 Use Case: Debugging + fallback UI.
errorCallback(error, stack) {
console.error('Error in LWC:', error, stack);
this.errorMessage = 'Something went wrong! Please try again later.';
}
✅ Helps you fail gracefully instead of breaking UI.
📊 Quick Reference Table
Lifecycle Hook | Timing | Common Use Case |
---|---|---|
constructor() | On creation | Initialize state, default values |
connectedCallback() | On DOM insertion | Fetch data, setup subscriptions |
renderedCallback() | After every render | DOM manipulation, libraries |
disconnectedCallback() | On DOM removal | Cleanup, unsubscribe |
errorCallback() | On error in component | Graceful error handling |
🎓 Real-Life Business Example: Student Attendance Dashboard
Imagine a Student Attendance Dashboard in Salesforce:
- constructor() → Default filter: “Today’s Attendance”
- connectedCallback() → Fetch attendance records from Apex
- renderedCallback() → Auto-scroll to latest student entry
- disconnectedCallback() → Unsubscribe from live attendance updates
- errorCallback() → Show fallback message if chart rendering fails
This ensures a smooth user experience, without memory leaks or runtime errors.
⚡ Best Practices to Remember
✅ Keep constructor() light → No DOM, no heavy logic.
✅ Use connectedCallback() → For API calls & subscriptions.
✅ renderedCallback() with caution → Guard with flags to avoid loops.
✅ Always cleanup in disconnectedCallback() → Prevent leaks.
✅ errorCallback() = friend → For user-friendly debugging.
🎯 Final Words
Lifecycle hooks aren’t just technical jargon — they’re the rhythm of your LWC’s life. Mastering them will help you:
✔ Build performant components
✔ Reduce bugs & crashes
✔ Deliver enterprise-grade Salesforce apps
👉 Next time you write an LWC, think: Which lifecycle hook is best for this job?
🔟 Frequently Asked Interview Questions on LWC Lifecycle Hooks
- What are Lifecycle Hooks in LWC? Why are they important?
👉 Interviewers expect you to explain the concept and how they control component creation, rendering, and cleanup. - When should you use
constructor()
in LWC? Can you call Apex methods inside it?
👉 Highlight that it’s only for initializing state, not for DOM or Apex calls. - Difference between
constructor()
andconnectedCallback()
. Which one is better for fetching data?
👉 Stress thatconnectedCallback()
is the right place for Apex calls and subscriptions. - What happens if you perform DOM manipulation inside
constructor()
?
👉 Expected answer: DOM is not yet available → it leads to runtime errors. - How does
renderedCallback()
differ fromconnectedCallback()
?
👉 Explain thatrenderedCallback()
executes after rendering and can run multiple times, whileconnectedCallback()
runs only once when added to the DOM. - How do you avoid infinite loops in
renderedCallback()
?
👉 Use a boolean flag (e.g.,this.isRendered
) to ensure DOM logic executes only once. - What is the purpose of
disconnectedCallback()
? Give a real-life scenario.
👉 Example: unsubscribing from a message channel or clearing setInterval when user navigates away. - Explain
errorCallback()
. How does it help in debugging and user experience?
👉 Expected: catches errors from child components, allows logging, or showing fallback UI. - Can you use all lifecycle hooks in a single LWC component? Would that be a good practice?
👉 Yes, but only if necessary. Emphasize best practices like keeping hooks lean and focused. - Real-world scenario: You’re building a Student Dashboard. Which lifecycle hooks would you use and why?
👉 This tests applied knowledge. You should explainconstructor()
for defaults,connectedCallback()
for fetching records,renderedCallback()
for scroll handling,disconnectedCallback()
for cleanup, anderrorCallback()
for handling chart errors.
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