Are you preparing for an interview on Lightning Web Components (LWC)? To help you ace your interview, we’ve compiled a comprehensive list of 30+ LWC scenario based interview questions experienced. These questions cover a wide range of topics, from component design and data interaction to events, error handling, and advanced component communication.
Whether you’re a experienced developer or freshers just starting out, this guide will provide you with the insights and knowledge you need to impress your interviewers and land your dream job.
Top 30+ LWC scenario based Interview Questions experienced
1. How would you design an LWC component to manage multiple child components dynamically?
2. Explain how you’d implement data binding between nested components in an LWC application.
3. Describe how you’d structure an LWC component to handle complex UI, such as multiple tabs or sections with conditional rendering.
Data and API Interaction
4. Explain how you’d design an LWC component to fetch and display records based on user input, considering performance and reusability.
5. How would you implement pagination in an LWC component that displays large data sets?
6. If you need to call a custom Apex method to retrieve data in an LWC component, how would you manage errors and handle caching?
7. Describe how you’d manage synchronous vs. asynchronous calls in LWC to optimize performance and user experience.
Events and Communication
8. In a parent-child LWC structure, how would you pass data from a child component back to the parent component?
9. Explain how you’d handle multiple event listeners for different components in an LWC application.
10. How would you prevent event propagation in an LWC component if you want to stop it at a certain level?
Lightning Data Service and Data Management
11. How would you handle data refresh in LWC after a record update using Lightning Data Service (LDS)?
12. Describe a scenario where you would use the lightning-record-edit-form vs. using custom Apex to update a record in LWC.
13. How would you handle optimistic UI updates in an LWC component while waiting for a server response?
Error Handling and Debugging
14. Describe your approach to handling errors from server-side Apex calls in LWC.
15. Explain how you’d debug an issue in LWC where data isn’t rendering correctly despite successful server calls.
Advanced Component Interaction and Composition
16. How would you pass a function from a parent component to a child component and use it in LWC?
17. Describe how you would create a reusable modal component in LWC that can be used across different pages.
18. How would you handle communication between sibling components in LWC?
Lightning Message Service (LMS) and Cross-Domain Communication
19. When would you use Lightning Message Service (LMS) in an LWC component, and how does it work?
20. Explain a use case for Lightning Message Service to synchronize data in real time across different LWC components.
Handling Complex Data Structures and Objects
21. How would you manage complex JSON data in an LWC component and display it efficiently?
22. How would you handle rendering and updating a list of records with different field values in an LWC component?
State Management and Performance Optimization
23. Describe how you would handle state management for an LWC component with multiple related fields.
24. How would you optimize an LWC component that displays data and often re-renders due to changes in unrelated state variables?
Custom Styling and Theming
25. How would you apply dynamic styling based on data in an LWC component?
26. Explain how you’d handle custom styling for an LWC component that needs to match different themes or brands.
Security and Access Control
27. How would you restrict access to certain fields in an LWC component based on user profile?
28. Describe how you would prevent a direct manipulation of a sensitive LWC component from the browser console.
Testing and Debugging
29. How would you unit test an LWC component that uses complex, asynchronous Apex calls?
30. Describe your approach to debugging a performance issue in LWC where the component becomes unresponsive.
31. How would you mock an external API call in LWC for testing purposes?
32. Explain how you’d test a component that dispatches a custom event in LWC.
Component Design and Structure
1. How would you design an LWC component to manage multiple child components dynamically?
Answer:
I would use the for:each directive in the parent component to dynamically render multiple instances of the child component. I would manage each child component’s unique properties by passing values through @api properties in the child. Additionally, if the child components need to communicate back to the parent, I would handle custom events for data propagation.
2. Explain how you’d implement data binding between nested components in an LWC application.
Answer:
In LWC, data binding is typically unidirectional. I would pass data down from the parent to the child components using @api properties in the child component. To send data back up, the child component would dispatch a custom event that the parent component listens for, effectively updating its state and allowing it to pass any necessary updated values back down to other children.
3. Describe how you’d structure an LWC component to handle complex UI, such as multiple tabs or sections with conditional rendering.
Answer:
For managing complex UIs with multiple sections or tabs, I would use conditional rendering with the if:true and if:false directives, toggling the visibility of each section based on a component state variable. Additionally, I might use the slot mechanism to allow flexibility in the UI, letting consumers of the component insert custom content into each section.
Data and API Interaction
4. Explain how you’d design an LWC component to fetch and display records based on user input, considering performance and reusability.
Answer:
I would use the @wire decorator with an Apex method that takes user input as parameters. To improve performance, I would debounce user input (e.g., with setTimeout) before calling the server. For reusability, I would make the input and display components modular, allowing other components to reuse the fetching logic by separating it into a standalone component.
5. How would you implement pagination in an LWC component that displays large data sets?
Answer:
I would use server-side pagination to load a specific number of records at a time, retrieving the next page when the user requests it. I’d keep track of the current page number and use a combination of limit and offset SOQL clauses in the Apex controller to fetch data. For performance, I might implement infinite scrolling, loading new records as the user scrolls down.
6. If you need to call a custom Apex method to retrieve data in an LWC component, how would you manage errors and handle caching?
Answer:
I’d use the @wire service with an error handler to catch any issues when calling the Apex method. I would handle errors by displaying user-friendly messages in the UI. For caching, I would use the refreshApex() function or Salesforce’s Storable actions to cache data, refreshing it only when necessary to reduce server calls.
7. Describe how you’d manage synchronous vs. asynchronous calls in LWC to optimize performance and user experience.
Answer:
Synchronous calls can impact performance, so for most data calls, I’d rely on asynchronous methods using Promises or async/await. When chaining multiple asynchronous calls, I’d use Promise.all() to run them in parallel when possible. For user experience, I’d show loading indicators to communicate ongoing processes to the user.
Events and Communication
8. In a parent-child LWC structure, how would you pass data from a child component back to the parent component?
Answer:
I would dispatch a custom event from the child component with the required data included in the detail property. The parent component would handle this event and update its state accordingly. This pattern allows the child component to remain reusable and not tightly coupled with the parent’s specific implementation.
9. Explain how you’d handle multiple event listeners for different components in an LWC application.
Answer:
In the parent component, I would use separate event listeners for each type of custom event. Each child component would dispatch its own specific events with unique names, allowing the parent component to differentiate and handle each accordingly. Alternatively, if handling similar events, I might pass specific data in the event’s detail property to identify the event source.
10. How would you prevent event propagation in an LWC component if you want to stop it at a certain level?
Answer:
I would use the stopPropagation() method within the event handler in the child component. This ensures that the event doesn’t bubble up past a specified component level. Additionally, using event.preventDefault() can stop any default behavior associated with the event, which is useful in some cases.
Lightning Data Service and Data Management
11. How would you handle data refresh in LWC after a record update using Lightning Data Service (LDS)?
Answer:
Using the refreshApex function allows for automatic refreshing of the data after an update. I would bind the LDS data to an @wire property and call refreshApex() after an update, ensuring the latest data is displayed. For a record form, I could also use the recordUpdated event to automatically handle refreshes.
12. Describe a scenario where you would use the lightning-record-edit-form vs. using custom Apex to update a record in LWC.
Answer:
lightning-record-edit-form is ideal when I need a quick, standard form for editing a record without complex logic. It automatically handles validations and errors, making it efficient for simple updates. Custom Apex is preferable when I need more control, such as implementing complex validations or updating multiple related records within a single transaction.
13. How would you handle optimistic UI updates in an LWC component while waiting for a server response?
Answer:
I’d update the UI immediately after initiating a server request to give users instant feedback, but without committing changes to the backend. Once the server confirms, I would finalize the UI update. If the server response fails, I’d revert to the previous state and show an error message to the user.
Error Handling and Debugging
14. Describe your approach to handling errors from server-side Apex calls in LWC.
Answer:
I’d use .catch() for Promises and error handling in @wire methods. For user-friendly error messages, I’d parse the message field from the error object and display it in the component UI. I would also log errors for debugging and troubleshooting, capturing the stack trace if necessary.
15. Explain how you’d debug an issue in LWC where data isn’t rendering correctly despite successful server calls.
Answer:
First, I’d check the server response to confirm the data’s format and structure. Then, I’d inspect the component’s JavaScript code, particularly any logic manipulating the data before rendering. Lastly, I’d examine the template’s conditional rendering or for:each directives to ensure data binding is properly implemented.
Advanced Component Interaction and Composition
16. How would you pass a function from a parent component to a child component and use it in LWC?
Answer:
LWC doesn’t support passing functions directly as properties like in some frameworks, but I can use events to achieve similar behavior. The parent component would register an event listener and execute its function when the child component dispatches a custom event, effectively triggering the desired function from the parent.
17. Describe how you would create a reusable modal component in LWC that can be used across different pages.
Answer:
I would create a generic modal component with slot tags to insert dynamic content. The modal would accept @api properties for controlling visibility and button actions. To use it across different pages, I would pass in the required content and actions through slot and @api attributes from the parent components, making the modal highly reusable.
18. How would you handle communication between sibling components in LWC?
Answer:
In LWC, sibling components cannot communicate directly. To enable communication, I would let the common parent handle events from one sibling and pass data or trigger actions in the other sibling. This way, the parent component serves as an intermediary, coordinating interactions between the siblings.
Lightning Message Service (LMS) and Cross-Domain Communication
19. When would you use Lightning Message Service (LMS) in an LWC component, and how does it work?
Answer:
LMS is useful for communication between components that don’t share a direct parent-child relationship, such as components on different pages or in separate tabs. I would define a message channel, publish messages from one component, and subscribe in the other component, allowing them to exchange data seamlessly.
20. Explain a use case for Lightning Message Service to synchronize data in real time across different LWC components.
Answer:
A common use case is a dashboard where multiple LWC components display related information. If a user updates data in one component, LMS can broadcast this update to other components so they can refresh automatically, keeping data in sync without direct connections between the components.
Handling Complex Data Structures and Objects
21. How would you manage complex JSON data in an LWC component and display it efficiently?
Answer:
For large or complex JSON data, I would parse it in the JavaScript controller and map it to a simplified structure that the template can handle easily. I might use recursive methods to process nested objects or arrays, using for:each and conditional rendering to display only relevant data, optimizing performance and readability.
22. How would you handle rendering and updating a list of records with different field values in an LWC component?
Answer:
I would use for:each to iterate over the list of records and if:true conditions to render specific fields dynamically. For updates, I would monitor changes in the data with a reactive property and update only modified records, potentially using Lightning Data Service (LDS) for efficiency.
State Management and Performance Optimization
23. Describe how you would handle state management for an LWC component with multiple related fields.
Answer:
I would create a single state object to hold related fields, updating specific properties as needed to minimize reactivity triggers. This approach helps maintain consistency and simplifies data management. For complex scenarios, I might implement a separate JavaScript class to manage state and logic, making it more organized.
24. How would you optimize an LWC component that displays data and often re-renders due to changes in unrelated state variables?
Answer:
I’d split the component into smaller components so that only parts of the UI directly affected by specific state variables re-render. Additionally, I’d use @track carefully, tracking only essential properties, and use computed properties to reduce unnecessary updates.
Custom Styling and Theming
25. How would you apply dynamic styling based on data in an LWC component?
Answer:
I’d bind CSS class names to JavaScript expressions or conditional logic in the component. I could use classMap in JavaScript to determine the CSS class based on the data, applying conditional styling in the template. For more complex cases, I’d dynamically set inline styles directly using JavaScript properties.
26. Explain how you’d handle custom styling for an LWC component that needs to match different themes or brands.
Answer:
I would create CSS variables and custom CSS classes for each theme, applying them dynamically based on a theme property or attribute passed from the parent. I’d also consider using SLDS tokens or custom properties to create a consistent look and feel across the application.
Security and Access Control
27. How would you restrict access to certain fields in an LWC component based on user profile?
Answer:
I would use field-level security (FLS) in Apex, checking the user’s permissions before sending data to the client. Alternatively, I could conditionally render fields based on user profile data available through @wire or Apex, displaying only allowed fields in the component.
28. Describe how you would prevent a direct manipulation of a sensitive LWC component from the browser console.
Answer:
I’d minimize the exposure of sensitive data in JavaScript variables, especially any values stored on the window object. Sensitive operations would be performed on the server-side via Apex, and I’d secure critical actions by validating user permissions in Apex controllers, preventing unauthorized access even if the UI is modified.
Testing and Debugging
29. How would you unit test an LWC component that uses complex, asynchronous Apex calls?
Answer:
I’d use Jest with the @salesforce/sfdx-lwc-jest module, mocking Apex calls with jest.mock to simulate server responses. By testing each scenario (success, failure, loading), I’d ensure the component handles data and errors correctly. For asynchronous behavior, I’d use async/await and Jest’s fake timers to control timing in my tests.
30. Describe your approach to debugging a performance issue in LWC where the component becomes unresponsive.
Answer:
I’d start by analyzing the component’s rendering cycles using the Chrome DevTools Performance panel. Then, I’d inspect my JavaScript logic for any intensive loops or computations and use console.time to measure execution times. I’d also check if reactive properties are causing excessive re-renders and refactor the component to improve performance.
31. How would you mock an external API call in LWC for testing purposes?
Answer:
In Jest, I’d create a mock for the external API function, replacing the real implementation with a simulated response. I’d use jest.fn() to mock the API call and return different test cases, verifying that the component correctly handles each case without actually calling the live API.
32. Explain how you’d test a component that dispatches a custom event in LWC.
Answer:
I’d use Jest to test the event by creating a mock listener function, attaching it to the parent component, and then dispatching the event in the child. I’d assert that the mock listener was called and validate that it received the expected event detail.
Learn More: Carrer Guidance [LWC scenario based Interview Questions experienced]
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