150 LWC Interview Questions and Answers for 2025

LWC Scenario-Based Interview Questions

These scenario-based LWC interview questions will help you demonstrate your practical experience and readiness to tackle challenges in the Salesforce ecosystem!

1. Scenario: You need to display a paginated list of records in LWC, but the list should only load more records when the user scrolls to the bottom. How would you achieve this?

This can be implemented using infinite scrolling. First, create a method that fetches records in chunks from the server (e.g., using Apex). Then, the onScroll event listener will detect when the user reaches the bottom of the list. When the bottom is detected, trigger the method to fetch more records and append them to the existing list.

2. Scenario: You are developing a custom data table that supports inline editing for a sales team. How would you handle validation for input fields in this table?

Use the lightning-datatable component’s built-in editable attribute to enable inline editing. For validation, use the oncellchange or onsave event to capture changes. Inside the event handler, you can use custom logic to validate fields (e.g., using setCustomValidity() and reportValidity() for lightning-input), then update the backend through an Apex method if validation passes.

3. Scenario: A user submits a form, but you want to prevent submission if certain conditions are not met, such as missing required fields. How would you handle this in LWC?

In the form submission event handler, iterate through the input fields and call their reportValidity() method. This ensures that all required fields and fields with validation constraints are checked. If reportValidity() returns false, prevent form submission. Additionally, you can use custom validation logic via setCustomValidity() for more specific checks.

4. Scenario: You must communicate between two sibling LWC components without a direct parent-child relationship. How would you manage this?

You can use the Lightning Message Service (LMS) for inter-component communication. First, create a message channel, then have one component publish messages to this channel and the other component subscribe to it. This allows both components to communicate without needing a direct parent-child relationship.

5. Scenario: A component fetches a large data set from the server. Users are experiencing slow performance due to the many records being displayed. How would you optimize this?

Implement lazy loading or pagination to load the data incrementally instead of all at once. You can fetch a small chunk of records (e.g., 20 records at a time) and load more data as the user scrolls (infinite scroll) or clicks a "Load More" button. This reduces the initial load time and improves performance.

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6. Scenario: You must build a reusable component that dynamically displays different record types. How would you handle this in LWC?

You can use the lightning-record-edit-form or lightning-record-view-form components, which dynamically generate forms based on the record type and object API name passed in. This component can be made reusable by using the @api decorator to accept record types and fields as inputs, allowing flexibility in the forms it generates.

7. Scenario: The data is not displaying correctly after rendering an LWC component. However, after the user interacts with the component, it updates as expected. What could be the issue, and how would you resolve it?

This is likely due to a reactivity issue. If you're working with complex data types (like objects or arrays), ensure you are using proper reactivity techniques. If the data is not updating correctly, you might need to either use the @track decorator to track internal property changes or ensure you create a new object/array reference after updating the data, as LWC relies on this to trigger re-renders.

8. Scenario: You want to retrieve and display a record's related list (e.g., opportunities related to an account) in an LWC component. How would you achieve this?

You can use an Apex method to retrieve related list data using a SOQL query that joins the parent and child objects (e.g., querying Opportunities with Account). Once the data is retrieved, display it using the lightning-datatable or a custom table component. You can also use getRelatedListRecords from the lightning/uiRelatedListApi module for simpler implementations.

9. Scenario: Your LWC component interacts with a third-party API to fetch real-time data. How would you handle errors that occur during the API call?

Use try...catch blocks around the API call (if using fetch() in JavaScript). Inside the catch() block, you can handle any errors, such as displaying a custom error message using lightning-toast or logging the error for debugging purposes. You can also implement retries if the API call fails due to network issues.

10. Scenario: You must implement a custom lookup field in an LWC component, similar to the standard Salesforce lookup field. How would you approach this?

Implement a custom lookup field using lightning-input for search input and lightning-combobox or a dropdown to display search results. Use an Apex method to perform the SOQL query and return search results based on user input. Debounce the search input to reduce unnecessary server calls and display the selected record as the lookup field’s value when chosen.

LWC Basic Interview Questions

Prepare yourself with the basic LWC interview questions that cover fundamental concepts and best practices.

1. What is Lightning Web Components (LWC)?

LWC is a modern UI framework built on native web standards for developing Lightning components in Salesforce. It leverages standard JavaScript, HTML, and CSS to create fast, efficient components. It runs natively in the browser and removes much of the framework overhead seen in its predecessor, Aura.

2. How is LWC different from Aura Components?

LWC is built on native web standards, making it lightweight and fast, while Aura components rely more on the Salesforce framework, making them heavier. LWC also uses modern JavaScript ES6+ features and performs better due to its simplified component lifecycle and smaller framework footprint.

3. What are the core files in an LWC component?

The core files in an LWC component are:

• .html: Defines the template or the UI.
• .js: Contains the logic of the component, written in JavaScript.
• .xml: Specifies the metadata and configurations for the component.

4. How do you create a simple Lightning Web Component?

You can create a Lightning Web Component using Salesforce CLI with the command sfdx force:lightning:component:create -n componentName -d force-app/main/default/lwc. This command generates the component’s folder with the necessary .html, .js, and .xml files.

5. What is the role of the .xml file in LWC?

The .xml file, also known as the configuration file, defines the metadata for the component, such as where the component can be used (e.g., Lightning App Builder, Record Pages, or Community Pages). It also specifies the target audience, access permissions, and other settings for the component.

6. Explain the @track decorator.

The @track decorator marks a property in the LWC JavaScript controller as reactive. When a tracked property changes, the component automatically re-renders, ensuring the UI stays in sync with the underlying data. In newer versions of LWC, this is mainly replaced with automatic reactivity for objects and arrays.

7. What is the @api decorator in LWC?

The @api decorator exposes a component's properties or methods to other components. It allows parent components to interact with child components by passing values or invoking methods.

8. What is one-way data binding in LWC?

One-way data binding in LWC means data flows in one direction—from the component’s JavaScript controller to the template. You can use curly braces {} in the template to reference a JavaScript property and render its value in the HTML.

9. Can LWC components interact with Aura components?

Yes, LWC components can interact with Aura components. An LWC can be embedded in an Aura component and vice versa. The two can communicate via events or public properties.

10. How do you handle events in LWC?

Events in LWC are handled using the standard JavaScript event model. You can dispatch an event from one component using the dispatchEvent method and listen for it in a parent component using an event handler in the HTML template (e.g., onclick).

11. What is the purpose of the connectedCallback() lifecycle hook?

The connectedCallback() method is invoked when the component is inserted into the DOM. It is similar to the connected() lifecycle hook in Aura components. This is typically used for tasks like initializing data or subscribing to events.

12. How does LWC handle conditional rendering?

LWC handles conditional rendering using the if:true and if:false directives in the template; for example, <template if:true={isVisible}> will render the block if the isVisible property is true.

13. How do you pass data from parent to child components?

Data is passed from a parent to a child component via public properties, marked with the @api decorator in the child component. The parent component can then bind values to these properties in its template.

14. What is Shadow DOM in LWC?

LWC uses Shadow DOM to encapsulate a component's styles and DOM structure, ensuring that they do not interfere with other components on the page.

15. Can you share CSS between Lightning Web Components?

No, each LWC component has its own encapsulated Shadow DOM, meaning styles are scoped to the component and cannot be shared directly. However, you can use the Lightning Design System (SLDS) for consistent component styling.

16. How do you make an LWC component available in the App Builder?

To make an LWC component available in the Lightning App Builder, specify the lightning__AppPage, lightning__RecordPage, or lightning__HomePage target in the component’s .xml file.

17. What are the limitations of LWC compared to Aura?

While LWC is lightweight and performs better than Aura, some legacy functionality, such as specific features of Locker Service, only exists in Aura components. Additionally, Aura components have built-in two-way data binding, while LWC only supports one-way data binding.

18. How do you define a custom event in LWC?

Custom events in LWC are created using the CustomEvent constructor. For example, const myEvent = new CustomEvent('myevent', { detail: someData }); can be dispatched using this.dispatchEvent(myEvent).

19. How do you handle errors in LWC?

Error handling in LWC can be done using try...catch blocks for synchronous code and .catch() methods for promises. Additionally, Salesforce provides an errorCallback() lifecycle hook for handling Lightning Message Service errors.

20. How do you use the lightning-record-form component in LWC?

The lightning-record-form is a base Lightning component that provides an easy way to view, create, and edit Salesforce records without needing custom Apex code. You can specify the recordId and objectApiName attributes to manage records automatically.

21. How do you import static resources in LWC?

Static resources in LWC can be imported using the @salesforce/resourceUrl import directive. For example: import myResource from '@salesforce/resourceUrl/myResource';.

22. What is the role of Locker Service in LWC?

Locker Service is a security feature in Salesforce that ensures Lightning components, including LWC, run in an isolated environment. It enforces strict security policies to prevent components from accessing unauthorized data.

23. Can LWC components be used in Visualforce pages?

Yes, LWC components can be embedded in Visualforce pages using the lightning:container Aura component, allowing for interaction between Visualforce and LWC.

24. How do you handle two-way data binding in LWC?

LWC does not have built-in two-way data binding like Aura. However, you can achieve two-way data binding by manually updating the state in the JavaScript controller in response to events from input elements.

25. What is the difference between connectedCallback() and renderedCallback()?

connectedCallback() is called when the component is added to the DOM, whereas renderedCallback() is called after the component has finished rendering. renderedCallback() may be called multiple times when the component re-renders.

26. How do you integrate LWC with Apex?

LWC can call Apex methods by importing them using @salesforce/apex/. You can use the @wire decorator in the JavaScript controller for reactive Apex calls or imperatively call Apex methods.

27. What are Lightning Data Service (LDS) benefits in LWC?

LDS allows you to interact with Salesforce data without writing Apex. It provides CRUD operations using built-in components like lightning-record-view-form and is cacheable, improving performance by reducing server calls.

28. How do you handle forms in LWC?

LWC supports forms using base components like lightning-input, lightning-button, and lightning-record-edit-form. These components automatically handle data binding and validation.

29. How do you use the lightning-datatable component?

The lightning-datatable component is used to display tabular data in LWC. It supports features like sorting, inline editing, and pagination. You can define columns and data for the table and manage actions like row selection.

30. What is a Lightning App in LWC?

A Lightning App is a custom standalone application built using LWC or Aura components. It is defined with a .app file and can be used independently of Salesforce pages to create custom UIs.

31. What is the role of Salesforce CLI in LWC development?

Salesforce CLI (Command Line Interface) is a powerful tool for developing LWC. It allows developers to create, deploy, and manage LWC components in Salesforce orgs using commands like sfdx force:lightning:component:create.

32. Can you debug LWC components in the browser?

Yes, LWC components can be debugged using standard browser developer tools (DevTools). Since LWC is built on web standards, you can inspect elements, set breakpoints, and debug JavaScript code directly.

33. What is the wire service in LWC?

The wire service is a reactive service in LWC that retrieves data from Salesforce. It automatically retrieves and updates the data when the underlying Salesforce data changes. You can connect to Apex methods, Salesforce objects, or LDS.

34. How do you set up unit testing for LWC?

LWC unit testing can be done using the @salesforce/sfdx-lwc-jest framework. Jest is a JavaScript testing framework that allows you to write unit tests for LWC components by mocking Salesforce-specific modules and asserting expected behavior.

35. How do you optimize LWC for performance?

Performance in LWC can be optimized by minimizing DOM manipulation, reducing network calls, using LDS caching, lazy loading components, and using the @wire decorator for reactive data loading.

36. How do you use getRecord in LWC?

The getRecord method from lightning/uiRecordApi is used in LWC to retrieve Salesforce record data without writing Apex. It uses LDS and can retrieve fields by specifying the record ID and object API name.

37. How do you bind a method to an event handler in LWC?

Using this keyword, you can bind a method to an event handler in LWC. In the HTML, you would use the format onclick={methodName} where methodName is a function in the component’s JavaScript controller.

38. How do you handle promises in LWC?

Promises in LWC are handled using the standard JavaScript then() and catch() methods or using async/await syntax for better readability in asynchronous code.

39. What are the security considerations in LWC?

LWC enforces security through Locker Service, which ensures that components operate in an isolated environment, preventing cross-component access. Additionally, it adheres to Salesforce's security model, respecting user permissions and sharing rules.

40. How do you deploy an LWC component to Salesforce?

LWC components are deployed to Salesforce using Salesforce CLI commands like sfdx force:source:deploy. You can also use change sets or packages to deploy components between orgs.

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LWC Interview Questions for Experienced

Dive deep into advanced concepts with this curated list of LWC interview questions tailored for experienced developers.

1. What is the lifecycle of a Lightning Web Component?

The LWC lifecycle has the following phases:

• constructor(): Invoked when the component is instantiated.
• connectedCallback(): Called when the component is added to the DOM.
• renderedCallback(): Executed after the component has rendered or re-rendered.
• disconnectedCallback(): Invoked when the component is removed from the DOM.
• errorCallback(error, stack): Called when an error occurs during rendering or in one of the lifecycle hooks.

Also Read: A Detailed Guide on Java Constructors

2. How does data binding work in LWC?

LWC uses one-way data binding, where data flows from the JavaScript class to the HTML template. The template uses curly braces {} to reference variables or methods from the JavaScript controller. Two-way data binding can be achieved using input fields and event handlers to capture user input and update the JavaScript properties accordingly.

3. How do you communicate between two LWC components?

LWC components can communicate through:

• Parent-child communication: Passing data from parent to child components using public properties (@api decorator) and invoking methods using the @api decorator.
• Child-parent communication: Using custom events (CustomEvent) to notify the parent component.
• Siblings' communication: This is via a parent component that serves as a mediator or uses Lightning Message Service (LMS).

4. What are wire adapters in LWC?

Wire adapters in LWC are built-in data providers that allow components to retrieve Salesforce data declaratively. The @wire decorator connects the component to Salesforce data, such as records, fields, or Apex methods. It supports reactive data fetching, automatically updating the component when the data changes.

5. How does Lightning Message Service (LMS) work in LWC?

LMS is a shared message service that facilitates communication between Lightning components (Aura and LWC) or Visualforce pages within the same Lightning page. You publish messages to a message channel, and any component subscribed to that channel can receive and process the message. LMS enables event-driven communication between components without requiring a direct parent-child relationship.

6. How do you handle Apex method calls in LWC?

LWC calls Apex methods in two ways:

• Imperatively: Using standard JavaScript functions and Promises to invoke Apex methods when needed.
• Declaratively: Using the @wire decorator to invoke Apex methods reactively, fetching data when the component is rendered or when specific property values change.

7. What is the purpose of @wire in LWC, and when would you use it?

The @wire decorator fetches reactive data in LWC. It connects the component to Salesforce data sources, such as records, fields, or Apex methods. It is useful when you want to automatically retrieve and update data based on component state or input parameters without writing imperative code.

8. How do you handle large data sets in LWC?

Handling large data sets in LWC involves techniques like:

• Pagination: Loading data in smaller chunks to avoid performance issues.
• Infinite scrolling: Dynamically loading more data as the user scrolls.
• Lazy loading: Loading data or components only when needed to reduce initial load times.
• Data table pagination: Using the lightning-datatable component to display and manage large data sets with pagination controls.

9. How does reactivity work in LWC?

In LWC, properties are reactive by default. If a property is a primitive (like a string or number), changes to its value automatically trigger the re-rendering of the component. For complex data types (like objects or arrays), reactivity can be enforced using the @track decorator or by creating a new reference to the object or array when modifying it.

10. How do you handle event propagation in LWC?

Event propagation in LWC is controlled using the bubbles and composed properties of the event. By default, events bubble up the DOM tree. If bubbles are set to true, the event bubbles up. If the composition is true, the event can propagate across shadow DOM boundaries, allowing it to be captured by parent components.

11. What is the significance of the renderedCallback() lifecycle hook?

The renderedCallback() method is called after the component's template has been rendered or re-rendered. It can perform post-rendering logic, such as manipulating the DOM, initializing third-party libraries, or performing actions based on the rendered state. It can be called multiple times if the component re-renders due to data changes.

12. How do you integrate third-party JavaScript libraries in LWC?

To integrate third-party JavaScript libraries in LWC, you must first upload the library as a static resource in Salesforce. Then, you can import the library using @salesforce/resourceUrl in your LWC component and load it dynamically using the loadScript or loadStyle methods from the lightning/platformResourceLoader module.

13. How do you perform field validation in LWC forms?

Field validation in LWC can be done using base Lightning components such as lightning input, which provides built-in validation for required fields, email formats, and number ranges. Custom validation can be added using the setCustomValidity() and reportValidity() methods on the input elements.

14. What are the differences between declarative and imperative Apex calls in LWC?

• Declarative: Uses the @wire decorator to bind the Apex method to a property. It is reactive and automatically re-executes when the tracked parameters change.
• Imperative: Uses the callApexMethod() function to invoke Apex explicitly in response to an event, such as a button click. It provides more control over when and how the Apex method is invoked.

15. How do you handle error handling in LWC?

Error handling in LWC can be achieved using:

• Try-catch blocks: For synchronous code.
• Promises .catch(): For handling rejected promises in asynchronous code.
• Apex Errors: The errorCallback() method captures errors during Apex calls.
• UI error handling: Displaying errors using lightning-toast messages or lightning-input error messages.

16. What is the difference between @track and reactive properties in LWC?

In early versions of LWC, the @track decorator was used to make properties reactive. However, primitive values (e.g., string, number, boolean) are now automatically reactive. If you want to track changes to their internal properties, the @track decorator is only required for complex objects (like arrays or objects).

17. How do you optimize LWC components for better performance?

• Use LDS to cache Salesforce records and reduce server requests.
• Lazy load components and data when they are needed.
• Debounce event handlers to prevent excessive event firing.
• Minimize DOM manipulation and ensure minimal re-renders.
• Use Lightning Message Service (LMS) for efficient communication between components.

18. How do you use lightning-datatable in LWC?

The lightning-datatable component is used to display tabular data in LWC. It supports sorting, inline editing, row selection, and pagination. You define the columns with metadata such as label and fieldName, and type and bind it to a data array that holds the row data.

19. What is the lightning/uiRecordApi module?

The lightning/uiRecordApi module provides declarative access to Salesforce data using Lightning Data Service. It includes wire adapters and functions like getRecord, getRecords, and createRecord to perform CRUD operations without writing Apex code.

20. How do you implement pagination in LWC?

Pagination in LWC can be implemented by dividing the data set into smaller chunks and loading only a subset of records at a time. You can either handle pagination on the client side by slicing the data array or use server-side pagination by fetching a specific number of records from Salesforce simultaneously.

21. How do you debug LWC components?

LWC components can be debugged using the browser DevTools, which provides access to the component's HTML, JavaScript, and network requests. You can set breakpoints, log variables, and inspect DOM elements. Salesforce also offers the lwc-recipes app with sample components for testing.

22. How do you manage component state in LWC?

State management in LWC is done by using component properties. Data can be passed into the component using public properties (@api), and the internal state can be managed with reactive properties that automatically trigger re-renders when their values change.

23. How do you use the Lightning Design System (SLDS) in LWC?

SLDS is used in LWC to apply Salesforce's design system styles. You can use SLDS classes in the LWC templates directly by applying them to HTML elements. For example, <div class="slds-box"> applies the SLDS box styling.

24. What are slots in LWC?

Slots in LWC allow you to define placeholders in a component's template where the parent component can pass its content. There are two types: default slots for single content injection and named slots for multiple content injections in predefined areas.

25. How do you use decorators in LWC?

LWC uses decorators like @api, @track, and @wire to enhance component functionality:

• @api: Exposes public properties and methods to parent components.
• @track: Marks properties as reactive (for objects and arrays).
• @wire: Binds the component to Salesforce data or Apex methods.

26. How do you define public properties in LWC?

Public properties in LWC are defined using the @api decorator in the JavaScript file. These properties allow parent components to pass data into the child component. For example:

javascript
Copy code
@api
myPublicProperty;

27. How do you handle multiple events in a single LWC component?

Multiple events in an LWC component can be handled by defining separate methods for each event in the JavaScript controller and binding these methods to the event listeners in the HTML template using onclick, onchange, etc.

28. How does Shadow DOM affect styling in LWC?

Shadow DOM encapsulates the styles and markup of a Lightning Web Component, preventing its internal styles from leaking into other components and vice versa. This ensures isolation but also means global CSS cannot directly affect components inside the Shadow DOM.

29. What are event phases in LWC?

The event phases in LWC follow the standard DOM event model:

• Capture phase: The event propagates from the window to the target element.
• Target phase: The event reaches the target element.
• Bubble phase: If the bubble property is true, the event bubbles back up from the target to the window.

30. How do you achieve cross-component LWC communication without a parent component?

Cross-component communication in LWC can be achieved using Lightning Message Service (LMS). LMS allows components to publish and subscribe to messages across the entire application, regardless of their parent-child relationship.

31. How do you cache data in LWC?

Data can be cached in LWC using Lightning Data Service (LDS), which caches data retrieved from Salesforce records. You can also implement custom caching logic in JavaScript by storing frequently accessed data in memory and only refreshing it when necessary.

32. How do you handle dynamic content rendering in LWC?

Dynamic content rendering in LWC can be achieved using JavaScript to manipulate the DOM or by conditionally rendering HTML blocks based on the state of reactive properties. You can also use lightning-dynamic-form for Salesforce record pages.

33. What is the getRecordNotifyChange method?

The getRecordNotifyChange() method from the lightning/uiRecordApi module notifies LDS that a record's data has changed. This method triggers LDS to refresh cached record data and update any components that rely on that record.

34. How do you handle data sharing between parent and child components in LWC?

Parent-child data sharing in LWC is done using public properties. The parent component can pass data to the child component by binding values to the child's public properties. The child component can expose methods for the parent to invoke using @api.

35. How do you work with lightning-record-edit-form in LWC?

lightning-record-edit-form is a base component providing a form layout for declarative editing or creating Salesforce records. You define the fields inside the form using lightning-input-field components, and the form automatically handles the save operation.

36. How do you use the lightning/uiListApi module?

The lightning/uiListApi module provides wire adapters like getListInfo and getListUi to retrieve Salesforce object list views and their records. These adapters allow you to display dynamic lists based on Salesforce list views.

37. How do you handle loading states in LWC?

Loading states in LWC can be managed using conditional rendering or by displaying a lightning-spinner component while data is being fetched. You can toggle the spinner's visibility using a Boolean flag, such as isLoading.

38. How do you use Apex in a Jest test for LWC?

In Jest tests for LWC, you cannot call real Apex methods. Instead, you mock Apex calls by importing the method and using the jest.mock() function to simulate the Apex method's behavior. This allows you to test the component logic without relying on server data.

39. How do you prevent memory leaks in LWC components?

Memory leaks in LWC can be prevented by:

• Cleaning up event listeners in the disconnectedCallback() lifecycle hook.
• Avoiding long-running or unnecessary event subscriptions.
• Properly managing component state and avoiding retaining references to unnecessary objects.

40. How do you handle permissions in LWC?

Permissions in LWC are handled by checking a user's access to Salesforce objects, fields, and records using wire adapters like getObjectInfo and getFieldValue. You can also use Apex to perform more complex permission checks based on custom logic.

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Advanced LWC Interview Questions

1. How does the Shadow DOM affect Lightning Web Components?

The Shadow DOM in LWC encapsulates the component's HTML, CSS, and JavaScript, ensuring styles and functionality are scoped to the component. This prevents styles from leaking out or other styles from affecting the component. LWC uses native Shadow DOM where supported and synthetic Shadow DOM where it isn’t. This isolation ensures a clean, modular structure for UI components.

2. What are the limitations of the Shadow DOM in LWC?

With the Shadow DOM, global CSS or JavaScript cannot directly modify the styles or content within a component. Another limitation is that elements inside the Shadow DOM are inaccessible from the global scope, making cross-component manipulation more complex. Additionally, native Shadow DOM is not fully supported by all browsers.

3. How do you perform unit testing for Lightning Web Components using Jest?

Jest is the recommended testing framework for LWC. You set up tests by creating a test folder in your LWC component directory and writing JavaScript test files that use Jest’s testing functions like describe(), it(), and expect(). Salesforce provides @salesforce/sfdx-lwc-jest to simplify the setup. Apex calls can be mocked using jest.mock().

4. How do you handle Apex callouts in LWC without blocking the UI?

In LWC, Apex callouts can be handled asynchronously using JavaScript Promises with either the .then() method or the async/await syntax. To ensure the UI remains responsive, you can display a spinner or loading indicator while the Apex call is in progress and hide it once the data is returned.

5. How do you create a reusable service component in LWC?

Exporting functions or classes from a standalone JavaScript file can create reusable service components in LWC. These components don’t have an HTML template, but they can perform logic like data transformations, utility functions, or API calls that can be imported and used across multiple components.

6. Explain the concept of event bubbling and composition in LWC.

Event bubbling in LWC allows events to propagate from the child element to the parent, eventually reaching the document root. By default, LWC supports bubbling but can be controlled using event properties like bubbles. Event composition allows the event to cross the boundary of the Shadow DOM when the composed property is set to true.

7. How do you optimize the performance of a complex LWC application?

Performance in LWC can be optimized by:

• Using Lazy Loading to load components or data only when needed.
• Leveraging Lightning Data Service (LDS) to minimize Apex calls and use cached data.
• Reducing DOM manipulation by updating only necessary elements.
• Debouncing event handlers to prevent unnecessary executions during user input.

8. How does Lightning Message Service (LMS) work, and how do you use it for inter-component communication?

LMS enables communication between LWC components, Aura components, and even Visualforce pages. Components can publish and subscribe to messages on a message channel. This event-driven mechanism decouples components from each other, making the architecture more modular. LMS is essential when components are not in a parent-child relationship but must share data.

9. Explain the importance of the @api, @track, and @wire decorators in LWC.

• @api: Exposes public properties and methods for the component to communicate with other components (usually parent-to-child communication).
• @track: Makes an object or array property reactive, ensuring UI updates when its internal state changes.
• @wire: Connects the component to Salesforce data (via Apex or LDS), providing automatic reactivity when the data changes.

10. How do you handle cross-component data communication using Pub/Sub in LWC?

Pub/Sub (publish-subscribe) is a pattern used to facilitate communication between components that are not directly related. In LWC, this can be achieved using custom event handlers or Lightning Message Service (LMS). A message is published by one component and subscribed to by another without needing a direct reference to each other.

11. What are dynamic imports in LWC, and how do they enhance performance?

Dynamic imports in LWC allow you to load JavaScript modules asynchronously, loading them only when needed. This technique enhances performance by reducing a component's initial load time. Dynamic imports are performed using JavaScript's import() function and are especially useful for large or rarely-used components.

12. How do you debug Lightning Web Components effectively in production?

In production, effective debugging of LWC components involves:

• Using console logging strategically to capture key information.
• Leveraging Salesforce’s built-in logging mechanisms such as Debug Logs or the Apex Debugger.
• Using browser Developer Tools to inspect the DOM, network requests, and component behavior.
• Creating detailed error messages using try-catch blocks.

13. How do you handle file uploads in LWC?

File uploads in LWC are handled using the lightning-file-upload component. This base component allows uploading files to Salesforce by specifying the record ID where the files will be linked. The component supports multiple file uploads, and you can use Apex to customize the upload behavior further or handle validation.

14. How do you implement custom validation in lightning-input?

You can implement custom validation in lightning-input using the setCustomValidity() method. This method sets a custom error message if the input doesn’t meet your conditions. The reportValidity() method is then called to display the error message and prevent form submission.

15. How do you handle bulk record processing in LWC?

Bulk record processing in LWC is managed by:

• Using pagination to handle large datasets efficiently.
• Implementing infinite scrolling or dynamic loading techniques.
• Using SOQL OFFSET or LIMIT in server-side queries to fetch data in smaller chunks.
• Using Apex for batch processing of records and retrieving results asynchronously in LWC.

16. What are the differences between lightning-record-edit-form and lightning-record-form?

• lightning-record-form: This form provides a quick way to create, edit, or display records without writing custom code. It includes all the necessary fields for a record.
• lightning-record-edit-form: Offers more granular control, allowing you to create custom forms for editing records. You can define each field individually and manage events like onload and onsuccess.

17. What is getRecord in the lightning/uiRecordApi module, and how is it used?

The getRecord function is part of the lightning/uiRecordApi module. It allows you to retrieve records using LDS without writing Apex. You specify the record ID, object API name, and fields you want to retrieve. This function is reactive, automatically updating when the record changes in Salesforce.

18. What is lightning-dynamic-form, and when would you use it?

The lightning-dynamic-form component allows developers to generate forms for Salesforce records declaratively, adapting dynamically to field-level security and layout changes. It simplifies the creation of record pages without hard-coding individual fields, allowing you to respond more easily to changes in object definitions.

19. How do you ensure security in LWC components?

Security in LWC components is enforced using Locker Service, which isolates components from each other and ensures they only access authorized resources. Additional security best practices include:

• Respecting CRUD and FLS (Field Level Security) using the lightning/uiRecordApi module or server-side checks.
• Avoiding direct DOM manipulation to prevent cross-site scripting (XSS) attacks.
• Using Apex controllers with proper security annotations.

20. How do you integrate LWC with third-party APIs?

Integration with third-party APIs in LWC is achieved by making HTTP requests using the fetch API in JavaScript. You can call external REST services from the client side. However, cross-origin resource sharing (CORS) must be handled appropriately, and sometimes Apex is used as a proxy to relay the data between the client and the third-party service.

21. What are slots in LWC, and how do they work?

Slots in LWC allow for component content customization by letting a parent component pass its content to a child component’s template. Slots are placeholders in the child component that get filled with content from the parent. Named slots can be used to control where specific content gets injected.

22. How do you handle multiple Apex methods in LWC?

Multiple Apex methods in LWC can be handled by importing them into the component and invoking them either imperatively or declaratively. You can manage multiple method calls concurrently using Promises or async/await, ensuring the data flow is managed efficiently without blocking the UI.

23. What are the key differences between @track and reactivity in modern LWC?

Initially, the @track decorator was used to make properties reactive in LWC. However, as of recent LWC updates, primitives like numbers, strings, and booleans are automatically reactive. The @track decorator is now primarily used to make changes to complex data types (like arrays and objects) that need to trigger UI re-renders.

24. How do you pass methods from parent to child components in LWC?

In LWC, methods cannot be passed directly from parent to child components. However, you can use custom events to trigger actions in the parent component from the child. Alternatively, you can define public methods in the child component using the @api decorator and call them from the parent component.

25. How do you manage component states in complex applications?

In complex applications, component state in LWC can be managed by:

• Using public properties to pass data between parent and child components.
• Leveraging Lightning Message Service (LMS) for cross-component communication.
• Managing internal state using reactive properties or tracking state changes using the @track decorator.

26. How does disconnectedCallback() differ from connectedCallback()?

connectedCallback() is called when the component is added to the DOM, typically used for initializing data or subscribing to events. disconnectedCallback() is triggered when the component is removed from the DOM, allowing you to clean up resources, unsubscribe from events, and prevent memory leaks.

27. How do you ensure accessibility in LWC?

Accessibility in LWC is ensured by following best practices, such as:

• Using semantic HTML elements.
• Implementing aria attributes where necessary.
• Providing keyboard navigation support.
• Using Salesforce’s SLDS classes that are already accessibility-compliant.

28. How do you configure custom events to stop event propagation in LWC?

Custom events in LWC can be configured to stop event propagation by calling event.stopPropagation() in the event handler. This method prevents the event from bubbling up the DOM, ensuring it is handled only by the intended component.

29. How do you handle data mutation in reactive properties in LWC?

Data mutation in reactive properties is managed by creating a new reference to the property instead of directly mutating it. The @track decorator helps ensure that internal changes trigger reactivity for arrays and objects. However, it’s best practice to use immutable data structures where possible.

30. What are custom data tables, and when would you build one in LWC?

Custom data tables are built when the standard lightning-datatable component does not meet specific requirements, such as complex row actions or custom cell rendering. You build custom tables using basic HTML and JavaScript, giving full control over the table’s structure and behavior.

31. How do you configure dynamic Apex method invocations in LWC?

Dynamic Apex method invocation in LWC involves parameters passed from the JavaScript controller to the server-side Apex method. The parameters can be changed dynamically based on user input or component state, allowing you to call different Apex methods or retrieve different data sets based on conditions.

32. What are the key performance bottlenecks in large-scale LWC applications?

Performance bottlenecks in large-scale LWC applications include:

• Excessive DOM manipulation.
• Unoptimized event listeners.
• Too many network calls.
• Lack of caching using Lightning Data Service (LDS).
• Not using lazy loading for components or data.

33. How do you implement inline editing in lightning-datatable?

Inline editing in lightning-datatable is achieved by enabling the editable attribute on the columns where you want to allow editing. You also handle events like onsave to manage data updates and send the updated data back to the server if necessary.

34. What is force:refreshView, and when would you use it?

force:refreshView is an Aura event used to refresh the data displayed by a component. In LWC, refreshing views or re-fetching data can be done using the getRecordNotifyChange method in LDS to refresh the data cache.

35. How do you handle multiple input validations in a form?

Multiple input validations in LWC forms are handled using the lightning-input component, which provides built-in validation for standard input types (e.g., email and number). For more complex validation rules, custom validation can be implemented using the setCustomValidity() and reportValidity() methods.

36. How do you prevent memory leaks in LWC?

Memory leaks in LWC can be prevented by:

• Unsubscribing from events is done using the disconnectedCallback() method.
• Avoiding long-lived references to DOM elements.
• Cleaning up timers and intervals when the component is removed from the DOM.

37. How do you handle two-way data binding in LWC?

LWC does not have built-in two-way data binding like Aura. However, you can simulate it using input event handlers (e.g., onchange or onclick) to capture user input and update the component’s internal state, thus syncing data between the UI and JavaScript.

38. How do you handle record deletion in LWC using LDS?

Record deletion in LWC using LDS is done via the deleteRecord method from the lightning/uiRecordApi module. You pass the record ID to the deleteRecord() function, and the record is removed from Salesforce while updating the LDS cache.

39. How do you create complex forms with conditional fields in LWC?

Complex forms with conditional fields in LWC are built using conditional rendering with if:true and if:false directives. You can show or hide fields based on the value of other form inputs, allowing for dynamic and interactive forms.

40. How do you handle search functionality in LWC?

Search functionality in LWC can be implemented using a lightning-input element to handle the onchange or onkeyup event. You can debounce the input to avoid unnecessary searches and call an Apex method or use LDS to search records based on the user input.

Conclusion

Mastering Lightning Web Components (LWC) is crucial for Salesforce and front-end developers aiming to stay ahead in 2025. This list of 120 LWC interview questions prepares you to tackle LWC challenges and land your dream job confidently. Whether you're refining your skills or preparing for your next role, LWC expertise will be key to your success in the Salesforce ecosystem.

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FAQs

1. What is LWC, and why is it used in Salesforce development?

Lightning Web Components (LWC) is a modern UI framework built on native web standards like JavaScript and HTML to develop Salesforce components. It is used because it is lightweight, faster, and leverages the latest web technologies, ensuring better performance and maintainability than older frameworks like Aura.

2. What are the key differences between Aura components and LWC?

LWC is built on native web standards and uses modern JavaScript (ES6+), while Aura is Salesforce's proprietary framework. LWC is lighter, more efficient, and performs better than Aura. Additionally, LWC uses a more simplified lifecycle and has lower framework overhead, whereas Aura relies on more Salesforce-specific abstractions.

3. What is the lifecycle of an LWC component?

The LWC lifecycle consists of key hooks:

• constructor(): Called when the component is instantiated.
• connectedCallback(): Invoked when the component is added to the DOM.
• renderedCallback(): Executed after rendering.
• disconnectedCallback(): Triggered when the component is removed from the DOM.
• errorCallback(): Handles errors during lifecycle events or rendering.

4. Why is Lightning Web Component (LWC) important in Salesforce development?

LWC is important because it improves performance and development efficiency using native web technologies, reduces complexity by minimizing the Salesforce-specific framework, and allows developers to build reusable, modular components. It aligns with modern web standards, making it a future-proof solution for Salesforce applications.

5. What are the key benefits of using LWC for Salesforce developers?

Key benefits of LWC include:

• Improved performance through lightweight components.
• Easier maintenance and faster development due to the use of native web standards.
• Better scalability and reusability of components.
• Seamless integration with existing Salesforce features like Lightning Data Service (LDS) and Lightning App Builder.