LWC Interview Questions with Practical Examples

Published On: May 16, 2026

Table of Contents

Complete Salesforce Lightning Web Components (LWC) Interview Guide

Lightning Web Components (LWC) is one of the most important topics in Salesforce developer interviews. Most companies now prefer LWC over Aura Components because it is faster, lightweight, modern, and based on web standards.

In interviews, candidates are often asked:

Difference between @wire and Imperative Apex
LDS vs Apex
Parent-child communication
Lifecycle hooks
Event handling
Reactive properties
Component communication scenarios

Many candidates know the theory but struggle to explain practical implementation with real examples.

This blog explains every important LWC concept in detail with practical examples and interview-focused explanations.

1. @wire vs Imperative Apex in LWC

This is one of the most frequently asked Salesforce LWC interview questions.

Interviewers usually ask:

What is @wire?
When should we use imperative Apex?
Difference between reactive and non-reactive calls?
Which one is better?
Can we call DML using @wire?

Understanding @wire in LWC

@wire is used to fetch data reactively.

Reactive means:

Whenever the parameter value changes, Salesforce automatically calls the Apex method again.

Key Features of @wire

Reactive
Automatic data refresh
Simpler syntax
Mostly used for read operations
Uses cacheable=true methods
Best for displaying data

@wire Architecture Flow

Image:

User Input → Reactive Parameter Changes → @wire Calls Apex → Data Returns Automatically → UI Updates

Example: Using @wire in LWC

Apex Class

public with sharing class AccountController {
    
    @AuraEnabled(cacheable=true)
    public static List<Account> getAccounts(String searchKey) {
        return [
            SELECT Id, Name, Industry
            FROM Account
            WHERE Name LIKE :('%' + searchKey + '%')
            LIMIT 10
        ];
    }
}

LWC JavaScript

import { LightningElement, wire, track } from 'lwc';
import getAccounts from '@salesforce/apex/AccountController.getAccounts';

export default class WireExample extends LightningElement {

    @track searchKey = '';

    @wire(getAccounts, { searchKey: '$searchKey' })
    accounts;

    handleChange(event) {
        this.searchKey = event.target.value;
    }
}

LWC HTML

<template>
    <lightning-input
        label="Search Account"
        onchange={handleChange}>
    </lightning-input>

    <template if:true={accounts.data}>
        <template for:each={accounts.data} for:item="acc">
            <p key={acc.Id}>{acc.Name}</p>
        </template>
    </template>
</template>

Important Interview Points about @wire

1. cacheable=true is mandatory

Without cacheable=true, @wire will throw an error.

Reason:

@wire is designed for read-only operations.

2. Reactive Variables

{ searchKey: '$searchKey' }

The $ symbol makes the property reactive.

Whenever searchKey changes:

Apex method executes again
UI refreshes automatically

3. Cannot Perform DML Using @wire

You cannot:

insert
update
delete

using @wire methods.

Because wired methods must be cacheable.

Understanding Imperative Apex

Imperative Apex means:

You manually call Apex whenever required.

Unlike @wire, it does not automatically execute when values change.

Key Features of Imperative Apex

Manual execution
Better control
Used for DML operations
Supports insert/update/delete
Used for button click operations
Used for complex logic

Imperative Apex Flow

Image:

Button Click → JavaScript Calls Apex → Promise Returns Response → UI Updates

Example: Imperative Apex

Apex Class

public with sharing class ContactController {

    @AuraEnabled
    public static List<Contact> getContacts(String accountId) {
        return [
            SELECT Id, Name, Email
            FROM Contact
            WHERE AccountId = :accountId
        ];
    }
}

LWC JavaScript

import { LightningElement, track } from 'lwc';
import getContacts from '@salesforce/apex/ContactController.getContacts';

export default class ImperativeExample extends LightningElement {

    @track contacts;

    handleLoad() {
        getContacts({ accountId: '001XXXXXXXXXXXX' })
            .then(result => {
                this.contacts = result;
            })
            .catch(error => {
                console.error(error);
            });
    }
}

Why Interviewers Prefer This Question

This question checks whether the candidate understands:

Reactive programming
Data handling
Caching
Performance optimization
Best practices

@wire vs Imperative Apex Comparison Table

Feature	@wire	Imperative Apex
Execution	Automatic	Manual
Reactive	Yes	No
cacheable=true Required	Yes	No
Supports DML	No	Yes
Better for Read Operations	Yes	Yes
Better Control	Limited	Full
Error Handling	Automatic + manual	Manual
Best Use Case	Display data	Button actions

Interview Scenario Question

Question

“When would you use Imperative Apex over @wire?”

Best Answer

Use Imperative Apex when:

We need DML operations
We need better control over execution
Data should not load automatically
We need to call Apex on button click
Complex business logic exists

2. LDS vs Apex in LWC

Another very important interview topic.

Interviewers ask:

What is Lightning Data Service?
Difference between LDS and Apex?
Which one performs better?
When should we avoid Apex?

What is Lightning Data Service (LDS)?

Lightning Data Service allows LWC components to work with Salesforce records without writing Apex.

Salesforce automatically handles:

CRUD
FLS
Sharing
Caching
Security

LDS Architecture

Image:

LWC → Lightning Data Service → Salesforce Database

Mention:

Security handled automatically
No Apex needed
Shared cache

Example: Using LDS

HTML

<template>
    <lightning-record-form
        record-id={recordId}
        object-api-name="Account"
        layout-type="Full"
        mode="view">
    </lightning-record-form>
</template>

JavaScript

import { LightningElement, api } from 'lwc';

export default class AccountRecord extends LightningElement {
    @api recordId;
}

Benefits of LDS

1. No Apex Required

Less code.

Less maintenance.

2. Automatic Security

LDS automatically enforces:

CRUD
Field-Level Security
Sharing Rules

3. Better Performance

Uses shared cache.

If another component already loaded the same record:

Salesforce reuses cached data.

When to Use Apex Instead of LDS

Use Apex when:

Complex SOQL is needed
Multiple objects involved
Aggregation required
Custom business logic needed
Large datasets involved

LDS vs Apex Comparison Table

Feature	LDS	Apex
Requires Apex Code	No	Yes
Security Handled Automatically	Yes	Manual
Complex Queries	No	Yes
Performance	Excellent	Depends
Multi-object Queries	Limited	Yes
Best for Simple Forms	Yes	No

Interview Tip

A strong developer always prefers:

LDS first
Apex only if required

Interviewers love hearing this.

3. Parent-Child Communication in LWC

This is one of the most practical LWC interview topics.

Interviewers ask:

How do components communicate?
Parent to child communication?
Child to parent communication?
Sibling communication?

Parent to Child Communication

Parent passes data using:

@api

Flow Diagram

Image:

Parent Component → Public Property (@api) → Child Component

Example: Parent to Child

Child Component JS

import { LightningElement, api } from 'lwc';

export default class ChildComponent extends LightningElement {
    @api message;
}

Child HTML

<template>
    <p>{message}</p>
</template>

Parent HTML

<template>
    <c-child-component message="Hello from Parent">
    </c-child-component>
</template>

Child to Parent Communication

Child communicates using:

Custom Events

Flow Diagram

Image:

Child Component → Custom Event → Parent Component

Example: Child to Parent

Child JS

import { LightningElement } from 'lwc';

export default class ChildComponent extends LightningElement {

    sendData() {
        const event = new CustomEvent('save', {
            detail: 'Record Saved'
        });

        this.dispatchEvent(event);
    }
}

Child HTML

<template>
    <lightning-button
        label="Send"
        onclick={sendData}>
    </lightning-button>
</template>

Parent HTML

<template>
    <c-child-component onsave={handleSave}></c-child-component>
</template>

Parent JS

import { LightningElement } from 'lwc';

export default class ParentComponent extends LightningElement {

    handleSave(event) {
        console.log(event.detail);
    }
}

Important Interview Concepts

event.detail

Used to pass data from child to parent.

dispatchEvent()

Used to fire custom events.

@api Decorator

Makes properties public.

Sibling Communication

Sibling components communicate using:

Lightning Message Service (LMS)
PubSub (older approach)

Interviewers often ask:

“Which is preferred?”

Correct Answer:

Lightning Message Service.

Lightning Message Service Architecture

Image:

Sibling Component A → Message Channel → Sibling Component B

4. Lifecycle Hooks in LWC

This is one of the most important concepts.

Interviewers frequently ask:

What are lifecycle hooks?
Difference between connectedCallback and renderedCallback?
When should we call Apex?
Which hook executes multiple times?

What are Lifecycle Hooks?

Lifecycle hooks are special JavaScript methods that execute automatically during component creation and destruction.

LWC Lifecycle Flow

Image:

Constructor → connectedCallback → render() → renderedCallback → disconnectedCallback

1. constructor()

This is the first method executed.

Used for:

Initializing variables
Basic setup

Example

constructor() {
    super();
    console.log('Constructor Called');
}

Important Interview Point

Never access DOM elements in constructor.

Because component is not rendered yet.

2. connectedCallback()

Called when component is inserted into DOM.

Best Uses

Call Apex
Initialize data
Subscribe to LMS
Setup listeners

Example

connectedCallback() {
    console.log('Component Inserted into DOM');
}

Interview Tip

Most developers call APIs inside:

connectedCallback()

3. renderedCallback()

Called after component rendering completes.

Important Concept

This hook can execute multiple times.

Reason:

Whenever reactive property changes, component rerenders.

Example

renderedCallback() {
    console.log('Component Rendered');
}

Common Interview Mistake

Candidates often create infinite loops inside renderedCallback.

Example:

renderedCallback() {
    this.name = 'Salesforce';
}

This causes continuous rerendering.

Correct Approach

Use boolean flag.

isRendered = false;

renderedCallback() {
    if(this.isRendered) {
        return;
    }

    this.isRendered = true;

    console.log('Executed Once');
}

4. disconnectedCallback()

Called when component is removed from DOM.

Best Uses

Cleanup code
Remove listeners
Unsubscribe LMS
Clear intervals

Example

disconnectedCallback() {
    console.log('Component Removed');
}

Lifecycle Hooks Comparison Table

Hook	Purpose
constructor	Initialize component
connectedCallback	Component added to DOM
renderedCallback	Component rendered
disconnectedCallback	Component removed

Frequently Asked LWC Interview Questions

1. Why is LWC faster than Aura?

Because LWC:

Uses native browser APIs
Lightweight framework
Better rendering engine
Less abstraction

2. Difference between @track and @api?

Decorator	Purpose
@api	Public property
@track	Reactive private property

3. Can we call Apex in constructor?

Technically possible but not recommended.

Use:

connectedCallback()

4. Which lifecycle hook executes multiple times?

renderedCallback()

5. Which communication method is best for unrelated components?

Lightning Message Service.

Real Interview Scenario Questions

Scenario 1

You need to display Account data automatically whenever search value changes.

Best Solution

Use:

@wire

Because it supports reactive data fetching.

Scenario 2

User clicks button and records should save.

Best Solution

Use:

Imperative Apex

Because DML operations are needed.

Scenario 3

You need simple record edit form.

Best Solution

Use:

Lightning Data Service

Scenario 4

Child component needs to notify parent after save.

Best Solution

Use:

Custom Events

Common Mistakes Candidates Make in Interviews

1. Confusing @wire with Imperative Apex

2. Forgetting cacheable=true

3. Calling DML using @wire

4. Infinite loops in renderedCallback

5. Using Apex when LDS is enough

Final Interview Preparation Tips

Focus on Practical Understanding

Interviewers prefer:

Real scenarios
Best practices
Performance optimization
Security understanding

more than memorized definitions.

Best Way to Answer LWC Interview Questions

Always explain:

What it is
Why it is used
When to use it
Real-world example
Best practices
Limitations

Conclusion

LWC interview questions are heavily focused on:

Real implementation
Component communication
Data handling
Performance optimization
Lifecycle understanding

The most important concepts every Salesforce developer should master are:

@wire
Imperative Apex
LDS
Parent-child communication
Lifecycle hooks
Lightning Message Service

If you understand these concepts deeply with practical examples, you can confidently answer most Salesforce LWC interview questions.

Recommended Practice Exercises

Build these mini projects:

Account Search using @wire
Contact Save using Imperative Apex
Record Form using LDS
Parent-child communication demo
LMS communication demo
Lifecycle hooks logger component

These projects will improve both:

Interview confidence
Real project skills

Best of Luck

Trusted by 2000+ learners to crack interviews at TCS, Infosys, Wipro, EY, and more.

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