Lightning Web Components (LWC) have swiftly emerged as a vital technology for creating efficient, modern, and high-performance web applications. With Salesforce’s push towards a more standardized web stack, mastering LWC has become crucial for developers aiming to stay ahead in the competitive job market. Whether you’re an experienced developer or a fresh graduate, these LWC interview questions can significantly boost your chances of landing a job.
Here’s a list of 25+ of the most frequently asked LWC (Lightning Web Components) interview questions along with brief answers.
LWC (Lightning Web Components) interview questions and answers
1. What is LWC (Lightning Web Components)?
2. Why was LWC introduced when Aura Components already existed?
3. What are the differences between Aura and LWC?
4. What are the key files in an LWC component bundle?
5. Explain the life cycle hooks in LWC?
6. How do you communicate between LWC components?
7. What is @api in LWC?
8. What is @track in LWC?
9. What is the difference between @track and @api?
10. How can you invoke Apex methods in LWC?
11. What is @wire?
12. What is the difference between wired and imperative Apex calls?
13. How can you handle events in LWC?
14. How do you create a custom event in LWC?
15. What is Lightning Message Service (LMS) in LWC?
16. What are slots in LWC?
17. What is the Lightning Data Service (LDS)?
18. How can you perform CRUD operations using LDS in LWC?
19. Explain reactivity in LWC.
20. What is Shadow DOM in LWC?
21. How do you use conditional rendering in LWC?
22. How do you apply CSS to an LWC component?
23. How do you share CSS across multiple LWC components?
24. How can you optimize performance in LWC?
25. What is the purpose of lightning-record-edit-form?
26. What are decorators in LWC?
27. What is two-way data binding in LWC?
1. What is LWC (Lightning Web Components)?
Answer:
LWC is a lightweight framework built by Salesforce that leverages modern web standards to build reusable components on the Salesforce Lightning platform.
2. Why was LWC introduced when Aura Components already existed?
Answer:
Aura components use a proprietary model, whereas LWC is built using web standards. LWC is faster, more efficient, and provides better performance, making it preferable for large-scale applications.
3. What are the differences between Aura and LWC?
Answer:
- Framework: Aura uses a proprietary framework, while LWC leverages standard web APIs.
- Performance: LWC offers better performance.
- Bundle Structure: Aura has a more complex bundle with many files, while LWC has fewer files and a simpler structure.
4. What are the key files in an LWC component bundle?
Answer:
.html: Defines the template structure..js: Contains the JavaScript logic..css(optional): Contains the styles..xml: Component configuration file defining metadata for the component.
5. Explain the life cycle hooks in LWC?
Answer:
- constructor(): Called when the component is initialized.
- connectedCallback(): Called when the component is added to the DOM.
- disconnectedCallback(): Called when the component is removed from the DOM.
- renderedCallback(): Called after the component has been rendered.
6. How do you communicate between LWC components?
Answer:
- Parent to Child: Via public properties (
@api). - Child to Parent: Using custom events.
- Sibling to Sibling: Using a shared state or via a parent component or the Lightning Message Service (LMS).
7. What is @api in LWC?
Answer:
The @api decorator is used to expose properties and methods to other components, making them publicly accessible.
8. What is @track in LWC?
Answer:
@track was previously used to make properties reactive in earlier versions of LWC, but now reactivity is automatic for all objects and primitive types.
9. What is the difference between @track and @api?
Answer:
- @api: Makes a property or method public for external use.
- @track: (Legacy) Tracks changes to an object’s internal state for reactivity within the component.
10. How can you invoke Apex methods in LWC?
Answer:
By importing and calling an Apex method using the @wire decorator or using imperative Apex call patterns (import { method } from '@salesforce/apex/Controller.method').
11. What is @wire?
Answer:
The @wire decorator is used to call an Apex method or interact with Salesforce data (like calling server-side code or fetching data from the server) in a reactive way.
12. What is the difference between wired and imperative Apex calls?
Answer:
- Wired: Automatically updates data when it changes and is reactive.
- Imperative: Manually calls the Apex method in JavaScript with control over when and how to call it.
13. How can you handle events in LWC?
Answer:
By using the standard event-handling mechanisms, such as addEventListener or custom events, with dispatchEvent.
14. How do you create a custom event in LWC?
Answer:
You can create a custom event by using new CustomEvent('eventName', { detail: data }) and dispatch it using dispatchEvent(event).
15. What is Lightning Message Service (LMS) in LWC?
Answer:
LMS is a messaging framework that allows LWC components to communicate across the DOM or with Aura components, even if they don’t share a direct relationship.
16. What are slots in LWC?
Answer:
Slots allow developers to pass HTML markup from a parent component into a child component. It is a way to enable content insertion in predefined locations in the child component.
17. What is the Lightning Data Service (LDS)?
Answer:
LDS provides access to Salesforce data and metadata without the need for Apex code. It is a framework to perform CRUD operations using lightning/ui* APIs in LWC.
18. How can you perform CRUD operations using LDS in LWC?
Answer: You can use lightning/uiRecordApi methods like:
getRecord(): To fetch a record.createRecord(): To create a record.updateRecord(): To update a record.deleteRecord(): To delete a record.
19. Explain reactivity in LWC.
Answer:
Reactivity in LWC means that changes to component properties or tracked objects automatically trigger updates in the DOM. In LWC, all primitive types are reactive, and objects are reactive without the need for @track.
20. What is Shadow DOM in LWC?
Answer:
The Shadow DOM encapsulates the component’s structure, style, and behavior, preventing it from affecting the DOM outside the component and vice versa. LWC uses a native or synthetic shadow DOM.
21. How do you use conditional rendering in LWC?
Answer:
You can use template directives like template if:true and template if:false to conditionally render elements.
22. How do you apply CSS to an LWC component?
Answer:
You can apply styles within the component’s .css file or use external stylesheets. Styles in the .css file are scoped to the component and won’t leak out due to the Shadow DOM.
23. How do you share CSS across multiple LWC components?
Answer:
You can create a Lightning Design System (SLDS) stylesheet or use static resources to share common styles across multiple components.
24. How can you optimize performance in LWC?
Answer:
- Use
@wirefor reactive data binding. - Avoid deeply nested loops.
- Minimize the number of re-renders by ensuring reactive properties are used efficiently.
- Use imperative Apex for one-time data loading.
25. What is the purpose of lightning-record-edit-form?
Answer:
lightning-record-edit-form is a base Lightning component used to create forms for editing or creating Salesforce records with fields that map to object fields.
26. What are decorators in LWC?
Answer:
- @api: Marks a field or method as public.
- @track: Tracks changes in an object’s internal state (now largely automatic).
- @wire: Links a property or method to a wire service for data handling.
27. What is two-way data binding in LWC?
Answer:
Unlike Aura, LWC does not support two-way data binding. Data flows one way, from the component to the DOM and from the DOM back to the component explicitly.
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