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Top 100 LWC Interview Questions and Answers

Top 100 LWC Interview Questions and Answers

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1. What is a Lightning Web Component (LWC)?

Answer:

A Lightning Web Component is a framework-agnostic UI component used in Salesforce development. It’s built on modern web standards and is part of the Salesforce Lightning Design System. LWCs can be used to build custom UI elements for Salesforce applications.

Official Salesforce LWC Documentation


2. How do you create a Lightning Web Component?

Answer:

To create a Lightning Web Component, you use the Salesforce CLI (Command Line Interface) with the sfdx force:lightning:component:create command. This generates the necessary files and directory structure for your component, including the JavaScript, HTML, and metadata files.

Official Salesforce CLI Documentation


3. What is the structure of a Lightning Web Component?

Answer:

A Lightning Web Component consists of three main files:

  1. JavaScript file (.js): Contains the JavaScript code for the component.
  2. HTML file (.html): Contains the markup for the component’s UI.
  3. XML file (.js-meta.xml): Contains metadata for the component, such as its label, description, and configuration.

Example:

// sampleComponent.js
import { LightningElement } from 'lwc';

export default class SampleComponent extends LightningElement {
    // JavaScript code goes here
}

Official LWC Component Documentation


4. How do you communicate between parent and child components in LWC?

Answer:

Parent and child components can communicate using properties. The parent component can pass data to the child component via HTML attributes, and the child component can emit events to notify the parent of any changes.

Example:

// Parent component HTML
<template>
    <c-child-component message={message}></c-child-component>
</template>

// Parent component JavaScript
import { LightningElement } from 'lwc';

export default class ParentComponent extends LightningElement {
    message = 'Hello from parent!';
}

Official LWC Communication Documentation


5. How do you handle events in Lightning Web Components?

Answer:

Events in Lightning Web Components are handled using a combination of the addEventListener method in JavaScript and custom events. The dispatchEvent method is used to fire an event from the child component, which can then be captured by the parent component.

Example:

// Child component JavaScript
handleClick() {
    const event = new CustomEvent('customclick', {
        detail: 'Button clicked!',
    });
    this.dispatchEvent(event);
}

// Parent component HTML
<template>
    <c-child-component oncustomclick={handleClick}></c-child-component>
</template>

// Parent component JavaScript
import { LightningElement } from 'lwc';

export default class ParentComponent extends LightningElement {
    handleClick(event) {
        const message = event.detail;
        // Handle the event data
    }
}

Official LWC Event Handling Documentation


6. How do you make an asynchronous callout in a Lightning Web Component?

Answer:

To make an asynchronous callout in an LWC, you use the fetch API or XMLHttpRequest in JavaScript. You can use the @wire decorator to wire the result of the callout to a property in your component.

Example using fetch:

import { LightningElement, wire } from 'lwc';

export default class SampleComponent extends LightningElement {
    @wire(getDataFromServer)
    dataFromServer;

    async getDataFromServer() {
        const response = await fetch('https://example.com/api/data');
        return await response.json();
    }
}

Official LWC HTTP Request Documentation


7. How do you handle errors in an asynchronous callout in Lightning Web Components?

Answer:

Errors in asynchronous callouts can be handled using try...catch blocks in JavaScript. You can catch exceptions and handle them appropriately, such as displaying an error message to the user.

Example:

async getDataFromServer() {
    try {
        const response = await fetch('https://example.com/api/data');
        if (!response.ok) {
            throw new Error('Network response was not ok');
        }
        return await response.json();
    } catch(error) {
        console.error('Error:', error);
        // Handle the error
    }
}

Official JavaScript Error Handling Documentation


8. How do you conditionally render elements in a Lightning Web Component?

Answer:

You can conditionally render elements in an LWC by using an if:true or if:false directive in the HTML template.

Example:

<template if:true={showElement}>
    This element is rendered when showElement is true.
</template>

<template if:false={showElement}>
    This element is rendered when showElement is false.
</template>

Official LWC Conditional Rendering Documentation


9. How do you iterate over a list of items in a Lightning Web Component?

Answer:

You can use the for:each directive in the HTML template to iterate over a list of items in an LWC.

Example:

<template for:each={items} for:item="item">
    <p key={item.id}>{item.name}</p>
</template>

In the corresponding JavaScript file, you should have a property named items which is an array of objects.

Official LWC Iteration Documentation


10. How do you handle user input in a Lightning Web Component?

Answer:

User input in an LWC is handled using event handlers. For example, you can use onchange for input fields and onclick for buttons. In the JavaScript file, define a method to handle the event.

Example:

<template>
    <lightning-input label="Name" onchange={handleInputChange}></lightning-input>
</template>
import { LightningElement } from 'lwc';

export default class SampleComponent extends LightningElement {
    handleInputChange(event) {
        this.name = event.target.value;
    }
}

Official LWC Event Handling Documentation


11. How do you use wire adapters in Lightning Web Components?

Answer:

Wire adapters are used to get data from a Salesforce org. They can be used to call Apex methods, get record data, and more. Use the @wire decorator to wire the data to a property.

Example:

import { LightningElement, wire } from 'lwc';
import { getRecord } from 'lightning/uiRecordApi';

export default class RecordComponent extends LightningElement {
    @wire(getRecord, { recordId: '$recordId', fields: ['Account.Name'] })
    account;
    // The account data is available in this.account.data
}

Official LWC Wire Adapters Documentation


12. How do you navigate to a different page in a Lightning Web Component?

Answer:

Use the NavigationMixin from the lightning/navigation module to navigate to a different page.

Example:

import { NavigationMixin } from 'lightning/navigation';

export default class NavigationExample extends NavigationMixin(LightningElement) {
    navigateToAccount() {
        this[NavigationMixin.Navigate]({
            type: 'standard__recordPage',
            attributes: {
                recordId: '001XXXXXXXXXXXXXXX',
                objectApiName: 'Account',
                actionName: 'view'
            }
        });
    }
}

Official LWC Navigation Documentation


13. How do you handle errors in a Lightning Web Component?

Answer:

Errors in Lightning Web Components can be handled using try-catch blocks in JavaScript. Additionally, you can display error messages in the UI to inform users of any issues.

Example:

try {
    // Code that may throw an error
} catch(error) {
    console.error('Error:', error);
    // Display an error message to the user
}

14. How can you use the Lightning Data Service in a Lightning Web Component?

Answer:

The Lightning Data Service (force:recordData) is used to retrieve, create, edit, or delete Salesforce records without requiring server-side code. You can use lightning-record-edit-form and lightning-record-view-form to work with records.

Example:

<lightning-record-edit-form
    object-api-name="Account"
    record-id={recordId}
    onsuccess={handleSuccess}
    onerror={handleError}>
    <!-- Fields go here -->
</lightning-record-edit-form>

Official Lightning Data Service Documentation


15. How do you implement event propagation in a Lightning Web Component?

Answer:

Event propagation in LWC can be achieved by dispatching and handling custom events. A parent component can listen for events dispatched by its child components, allowing for communication between them.

Example:

// Child component
this.dispatchEvent(new CustomEvent('myevent', { detail: 'Event data' }));

// Parent component HTML
<c-child-component onmyevent={handleEvent}></c-child-component>

// Parent component JavaScript
handleEvent(event) {
    const eventData = event.detail;
    // Handle the event data
}

16. What is the difference between @track and @api in Lightning Web Components?

Answer:

@track is used to mark a property as reactive, meaning any changes to that property will trigger a re-render of the component. @api is used to expose a property or method in a Lightning Web Component to be used in a parent component.

Example:

// @track usage
@track message = 'Hello World';

// @api usage
@api
showMessage() {
    console.log(this.message);
}

Official LWC @track Documentation

Official LWC @api Documentation


17. How do you use third-party libraries in a Lightning Web Component?

Answer:

You can use third-party libraries in an LWC by including them in a static resource and importing them using the @salesforce/resourceUrl directive. Then, you can load and use the library in your component.

Example:

import LIBRARY_NAME from '@salesforce/resourceUrl/LIBRARY_NAME';

// Load the library
loadScript(this, LIBRARY_NAME + '/library.js')
    .then(() => {
        // Use the library
    });

Official LWC Third-Party Library Documentation


18. How do you handle CSS styling in a Lightning Web Component?

Answer:

CSS styling in Lightning Web Components can be applied either at the component level using a CSS file or inline within the component’s HTML file. You can also leverage the Salesforce Lightning Design System (SLDS) for consistent styling.

Example:

/* SampleComponent.css */
.my-custom-style {
    color: red;
}
<!-- SampleComponent.html -->
<template>
    <div class="my-custom-style">Styled element</div>
</template>

Official LWC Styling Documentation


19. How do you use conditional rendering in a Lightning Web Component?

Answer:

Conditional rendering in LWC is achieved using directives like if:true and if:false. These directives determine whether a section of markup should be rendered based on a Boolean condition.

Example:

<template if:true={shouldRender}>
    This section is rendered if shouldRender is true.
</template>

<template if:false={shouldRender}>
    This section is rendered if shouldRender is false.
</template>

20. How do you implement server-side caching in a Lightning Web Component?

Answer:

Server-side caching in LWC can be implemented by using the cacheable attribute on an Apex method. This allows the result of the method to be cached on the server and reused for subsequent requests.

Example:

@AuraEnabled(cacheable=true)
public static List<Account> getAccounts() {
    return [SELECT Id, Name FROM Account];
}

Official LWC Server-Side Caching Documentation


21. How do you use base components in a Lightning Web Component?

Answer:

Base components in LWC are pre-built UI elements provided by Salesforce. You can use them to build the UI of your component. For example, lightning-input is a base component used for input fields.

Example:

<template>
    <lightning-input label="First Name" value={firstName}></lightning-input>
</template>

Official LWC Base Components Documentation


22. How do you implement pagination in a Lightning Web Component?

Answer:

Pagination in LWC can be implemented by keeping track of the current page and the number of items per page. Use JavaScript to calculate the range of items to display.

Example:

// Assuming itemsPerPage and currentPage are properties in the component
get displayedItems() {
    const start = (this.currentPage - 1) * this.itemsPerPage;
    const end = start + this.itemsPerPage;
    return this.items.slice(start, end);
}

Official LWC Pagination Documentation


23. How do you communicate between sibling components in a Lightning Web Component?

Answer:

Sibling components can communicate through a common ancestor component. The parent component can act as a mediator by receiving events from one sibling and passing data to the other.

Example:

// Sibling 1 (Sender)
this.dispatchEvent(new CustomEvent('customevent', { detail: 'Data to send' }));

// Parent Component
<template>
    <c-sibling-1 oncustomevent={handleEvent}></c-sibling-1>
    <c-sibling-2 data={data}></c-sibling-2>
</template>

// Parent Component JavaScript
handleEvent(event) {
    this.data = event.detail;
}

24. How do you handle security in a Lightning Web Component?

Answer:

Security in Lightning Web Components is primarily handled by Salesforce platform security. Ensure that users have the appropriate permissions to access and modify data. Additionally, use CRUD and FLS checks in Apex code.

Official Salesforce Security Documentation


25. How do you implement lazy loading of components in a Lightning Web Component?

Answer:

Lazy loading of components can be achieved using the loadScript and loadStyle functions from the lightning/platformResourceLoader module. This allows you to load resources only when they are needed.

Example:

import { loadScript, loadStyle } from 'lightning/platformResourceLoader';
import MY_SCRIPT from '@salesforce/resourceUrl/myScript';

// Inside a method or lifecycle hook
loadScript(this, MY_SCRIPT)
    .then(() => {
        // Script is loaded and can be used
    });

Official LWC Lazy Loading Documentation


26. How do you integrate a Lightning Web Component with a Visualforce page?

Answer:

You can use the lightning:container Aura component to embed an LWC in a Visualforce page. This enables you to leverage LWC’s capabilities within a Visualforce context.

Example:

<aura:component>
    <lightning:container aura:id="container" src="{!$Resource/myLWC}/main.html"/>
</aura:component>

Official LWC Integration with Visualforce Documentation


27. How do you handle events in a Lightning Web Component when using composition?

Answer:

When using composition, events can be handled by passing event handlers as properties to child components. The child component can then trigger these handlers when needed.

Example:

// Parent Component HTML
<c-child-component oncustomclick={handleClick}></c-child-component>

// Parent Component JavaScript
handleClick(event) {
    // Handle the event
}

Official LWC Event Handling Documentation


28. How do you handle error boundaries in a Lightning Web Component?

Answer:

Error boundaries in LWC are handled by using try-catch blocks in the JavaScript code. You can catch errors and handle them gracefully, preventing the entire component from failing.

Example:

try {
    // Code that may throw an error
} catch(error) {
    // Handle the error
    console.error('Error:', error);
}

29. How can you dynamically load metadata in a Lightning Web Component?

Answer:

You can use the getPicklistValuesByRecordType and getObjectInfo wire adapters to dynamically load metadata based on record types. This allows you to retrieve picklist values and object information at runtime.

Example:

import { getPicklistValuesByRecordType, getObjectInfo } from 'lightning/uiObjectInfoApi';

// Inside a wire method
@wire(getPicklistValuesByRecordType, { objectApiName: 'Account', recordTypeId: '$recordTypeId' })
picklistValues;

@wire(getObjectInfo, { objectApiName: 'Account' })
objectInfo;

Official LWC Dynamic Metadata Loading Documentation


30. How do you use the Salesforce Connect API in a Lightning Web Component?

Answer:

Salesforce Connect allows you to integrate external data sources into Salesforce. You can use the lightning:externalObject Aura component or lightning/uiObjectInfoApi to work with external objects in LWC.

Example (Using lightning/uiObjectInfoApi):

import { getObjectInfo } from 'lightning/uiObjectInfoApi';

// Inside a wire method
@wire(getObjectInfo, { objectApiName: 'MyExternalObject__x' })
objectInfo;

Official Salesforce Connect Documentation


31. How do you implement client-side caching in a Lightning Web Component?

Answer:

Client-side caching in LWC can be implemented using browser storage mechanisms like localStorage or sessionStorage. This allows you to store data on the client side for faster access.

Example:

// To store data
localStorage.setItem('key', 'value');

// To retrieve data
const value = localStorage.getItem('key');

MDN Web Docs on Web Storage


32. How do you use static resources in a Lightning Web Component?

Answer:

You can use static resources to store files like JavaScript, CSS, and images. Import the resources using @salesforce/resourceUrl and use them in your component.

Example:

import MY_JS_FILE from '@salesforce/resourceUrl/myJsFile';

// Load the JavaScript file
loadScript(this, MY_JS_FILE + '/script.js')
    .then(() => {
        // Script is loaded and can be used
    });

Official Salesforce Static Resources Documentation


33. How do you use custom labels in a Lightning Web Component?

Answer:

Custom labels can be used in LWC by importing them from the Salesforce organization. This allows you to use localized labels in your component.

Example:

import MY_LABEL from '@salesforce/label/c.myLabel';

// Access the label
const labelValue = MY_LABEL;

Official LWC Custom Labels Documentation


34. How do you handle component initialization in a Lightning Web Component?

Answer:

Component initialization can be handled in the connectedCallback() lifecycle hook. This is where you can perform setup tasks like loading data or setting default values.

Example:

connectedCallback() {
    // Initialization tasks
}

Official LWC Lifecycle Hooks Documentation


35. How can you use Apex wire methods in a Lightning Web Component?

Answer:

Apex wire methods allow you to call server-side Apex methods and retrieve data in a reactive manner. This is achieved using the @wire decorator.

Example:

import { wire, api } from 'lwc';
import getAccountList from '@salesforce/apex/MyController.getAccountList';

export default class MyComponent extends LightningElement {
    @wire(getAccountList, { param: '$property' })
    accounts;
}

Official LWC Wire Adapter Documentation


36. How do you create a record using Apex in a Lightning Web Component?

Answer:

Creating a record in LWC is done by calling an Apex method annotated with @AuraEnabled and passing the necessary data.

Example:

import createAccount from '@salesforce/apex/MyController.createAccount';

// Inside a method
createAccount({ Name: 'New Account Name' })
    .then(result => {
        // Handle the result
    })
    .catch(error => {
        // Handle the error
    });

Official Salesforce Apex Documentation


37. How do you implement client-side validation in a Lightning Web Component?

Answer:

Client-side validation in LWC is done using JavaScript. You can validate user input and display error messages if the input is invalid.

Example:

validateInput() {
    const inputValue = this.template.querySelector('input').value;
    if (inputValue.length < 5) {
        // Display error message
    }
}

38. How do you handle events in a Lightning Web Component when using pub-sub?

Answer:

When using pub-sub pattern in LWC, you can create a custom event and a central event bus to publish and subscribe to events across components.

Example:

// Event Bus (central place to handle events)
import { LightningElement, wire } from 'lwc';
export const EventBus = new LightningElement({});

// Component 1 (Publisher)
const event = new CustomEvent('customEvent', { detail: 'Data to send' });
this.dispatchEvent(event);

// Component 2 (Subscriber)
import { EventBus } from 'c/eventBus';
EventBus.dispatchEvent(new CustomEvent('customEvent'));

39. How do you handle asynchronous operations in a Lightning Web Component?

Answer:

Asynchronous operations in LWC are handled using JavaScript Promises, async/await, and callback functions. This allows you to perform tasks like making API calls or handling timeouts.

Example using Promises:

myAsyncFunction()
    .then(result => {
        // Handle the result
    })
    .catch(error => {
        // Handle the error
    });

40. How do you deploy a Lightning Web Component to a Salesforce org?

Answer:

To deploy an LWC, you can use Salesforce CLI or deploy it through Salesforce Setup. Make sure the component is included in the deployment package.

Example using Salesforce CLI:

sfdx force:source:deploy -m LightningComponentBundle:MyComponent

Official Salesforce CLI Documentation


41. How do you use JavaScript getters and setters in a Lightning Web Component?

Answer:

Getters and setters in LWC are used to intercept access to a property. They allow you to perform actions before getting or setting a value.

Example:

// Getter
get fullName() {
    return this.firstName + ' ' + this.lastName;
}

// Setter
set fullName(value) {
    [this.firstName, this.lastName] = value.split(' ');
}

MDN Web Docs on Getters and Setters


42. How do you perform unit testing for a Lightning Web Component?

Answer:

Unit testing in LWC is done using Jest, a JavaScript testing framework. You can write test cases for your component’s JavaScript and HTML files.

Example:

// Jest test file
import { createElement } from 'lwc';
import MyComponent from 'c/myComponent';

describe('c-my-component', () => {
    it('renders correctly', () => {
        const element = createElement('c-my-component', { is: MyComponent });
        document.body.appendChild(element);
        expect(element).toMatchSnapshot();
    });
});

Official LWC Jest Testing Documentation


43. How do you handle conditional rendering in a Lightning Web Component?

Answer:

Conditional rendering in LWC is achieved using JavaScript logic within the template. You can use if directives or the conditional operator to conditionally render elements.

Example using if directive:

<template if:true={shouldRender}>
    <!-- Content to render when shouldRender is true -->
</template>

Official LWC Conditional Rendering Documentation


44. How do you dynamically add or remove CSS classes in a Lightning Web Component?

Answer:

You can dynamically add or remove CSS classes in LWC using JavaScript by manipulating the classList property of an element.

Example:

// Add class
this.template.querySelector('.element').classList.add('new-class');

// Remove class
this.template.querySelector('.element').classList.remove('old-class');

MDN Web Docs on classList


45. How do you implement client-side pagination in a Lightning Web Component?

Answer:

Client-side pagination in LWC can be implemented by managing a subset of data and updating it based on user interactions like clicking next or previous.

Example:

// Assuming data is an array of records
const pageSize = 10;
let currentPage = 1;
let displayedData = data.slice((currentPage - 1) * pageSize, currentPage * pageSize);

46. How do you handle parent-child communication in a Lightning Web Component?

Answer:

Parent-child communication in LWC can be achieved by passing data from the parent component to the child component using properties.

Example:

<!-- Parent Component -->
<c-child-component data={parentData}></c-child-component>

<!-- Child Component -->
@api data;

Official LWC Property Documentation


47. How do you use external libraries or frameworks in a Lightning Web Component?

Answer:

You can use external libraries or frameworks in LWC by loading them as static resources and then importing and using them in your component.

Example:

import EXTERNAL_LIBRARY from '@salesforce/resourceUrl/externalLibrary';

// Load the library
loadScript(this, EXTERNAL_LIBRARY + '/library.js')
    .then(() => {
        // Library is loaded and can be used
    });

Official LWC External Libraries Documentation


48. How do you handle user authentication and authorization in a Lightning Web Component?

Answer:

User authentication and authorization in LWC are typically managed by Apex controllers. You can call server-side methods to verify user credentials and check permissions.

Example:

import authenticateUser from '@salesforce/apex/MyController.authenticateUser';

authenticateUser({ username, password })
    .then(result => {
        if (result === 'Authorized') {
            // User is authenticated and authorized
        } else {
            // Authentication failed
        }
    })
    .catch(error => {
        // Handle the error
    });

49. How do you handle component re-rendering in a Lightning Web Component?

Answer:

Component re-rendering in LWC can be controlled using the render() method. You can conditionally decide whether or not to re-render the component.

Example:

render() {
    return this.shouldRender ? super.render() : null;
}

Official LWC Rendering Lifecycle Documentation


50. How do you make an HTTP request in a Lightning Web Component?

Answer:

You can make HTTP requests in LWC using the fetch API or the XMLHttpRequest object to call external services or APIs.

Example using fetch:

fetch('https://api.example.com/data')
    .then(response => {
        if (!response.ok) {
            throw new Error('HTTP error');
        }
        return response.json();
    })
    .then(data => {
        // Handle the response data
    })
    .catch(error => {
        // Handle the error
    });

MDN Web Docs on Fetch API


51. How do you use Lightning Data Service in a Lightning Web Component?

Answer:

Lightning Data Service (LDS) allows you to work with Salesforce data without writing Apex code. You can use force:recordData in Aura components or the getRecord wire adapter in LWC to retrieve and update records.

Example using getRecord:

import { getRecord } from 'lightning/uiRecordApi';

@wire(getRecord, { recordId: '$recordId', fields: FIELDS })
account;

Official LWC Lightning Data Service Documentation


52. How do you implement responsive design in a Lightning Web Component?

Answer:

Responsive design in LWC can be implemented using CSS media queries. Define styles for different screen sizes to ensure your component looks and functions well on various devices.

Example CSS:

@media (max-width: 768px) {
    /* Styles for small screens */
}

MDN Web Docs on CSS Media Queries


53. How do you handle error handling and display error messages in a Lightning Web Component?

Answer:

Error handling in LWC can be done using try-catch blocks or by checking the error property returned from an asynchronous operation.

Example with try-catch:

try {
    // Code that might throw an error
} catch(error) {
    // Handle the error
    console.error(error);
    this.error = error.message; // Set error message in component state
}

54. How do you perform client-side caching in a Lightning Web Component?

Answer:

Client-side caching in LWC can be implemented using browser storage mechanisms like localStorage or sessionStorage to store and retrieve data.

Example using localStorage:

// To set data
localStorage.setItem('key', 'value');

// To get data
const value = localStorage.getItem('key');

MDN Web Docs on Web Storage


55. How do you handle file uploads in a Lightning Web Component?

Answer:

File uploads in LWC are typically handled by calling a server-side method that handles the file upload. You can use the lightning-file-upload component for the UI part.

Example:

<lightning-file-upload label="Attach receipt"
    name="fileUploader"
    accept={acceptedFormats}
    record-id={recordId}
    onuploadfinished={handleUploadFinished}>
</lightning-file-upload>

Official LWC File Upload Documentation


56. How do you use SLDS (Salesforce Lightning Design System) in a Lightning Web Component?

Answer:

You can use SLDS in LWC by importing the SLDS stylesheets and using SLDS class names in your component’s HTML markup.

Example:

<template>
    <div class="slds-card">
        <h1 class="slds-text-heading_large">SLDS Card</h1>
    </div>
</template>

Official SLDS Documentation


57. How do you implement pagination with server-side data retrieval in a Lightning Web Component?

Answer:

Pagination with server-side data retrieval in LWC involves using a combination of Apex methods and client-side logic to fetch and display data in chunks.

Example:

// Call server to get paginated data
getPaginatedData({ pageNumber, pageSize })
    .then(result => {
        // Process the result
    })
    .catch(error => {
        // Handle the error
    });

58. How do you implement lazy loading of images in a Lightning Web Component?

Answer:

Lazy loading of images in LWC can be achieved by setting the loading attribute of the <img> tag to “lazy”. This defers loading of images until they are about to become visible.

Example:

<img src="image.jpg" alt="Image" loading="lazy">

MDN Web Docs on Loading Attribute


59. How do you handle long-running operations in a Lightning Web Component?

Answer:

Long-running operations in LWC can be managed using JavaScript’s asynchronous programming features like Promises or async/await. You can show loading indicators while the operation is in progress.

Example using Promises:

// Show loading indicator
this.isLoading = true;

myLongRunningOperation()
    .then(result => {
        // Handle the result
    })
    .catch(error => {
        // Handle the error
    })
    .finally(() => {
        // Hide loading indicator
        this.isLoading = false;
    });

60. How do you handle cross-browser compatibility in a Lightning Web Component?

Answer:

Cross-browser compatibility in LWC is ensured by writing code that adheres to web standards and testing in multiple browsers. You can use feature detection and polyfills for unsupported features.

Example for feature detection:

if ('IntersectionObserver' in window) {
    // Use IntersectionObserver for certain functionality
} else {
    // Use fallback code
}

61. How do you implement server-side pagination in a Lightning Web Component?

Answer:

Server-side pagination in LWC involves making multiple requests to the server to fetch a subset of data based on page number and page size.

Example:

// Call server to get paginated data
getPaginatedData({ pageNumber, pageSize })
    .then(result => {
        // Process the result
    })
    .catch(error => {
        // Handle the error
    });

62. How do you implement keyboard accessibility in a Lightning Web Component?

Answer:

Keyboard accessibility in LWC is achieved by ensuring that all interactive elements can be navigated and activated using the keyboard alone. You can use the tabindex attribute and handle keyboard events.

Example:

<button tabindex="0" onclick={handleClick}>Click me</button>

MDN Web Docs on Keyboard Accessibility


63. How do you handle internationalization (i18n) in a Lightning Web Component?

Answer:

Internationalization in LWC involves using the Intl object to format dates, numbers, and strings based on the user’s locale.

Example for formatting a date:

const date = new Date();
const formattedDate = new Intl.DateTimeFormat('en-US').format(date);

MDN Web Docs on Intl


64. How do you implement a toast notification in a Lightning Web Component?

Answer:

You can implement a toast notification in LWC by dispatching an event that is handled by a higher-level component or by using a third-party library like lightning/platformShowToastEvent.

Example using lightning/platformShowToastEvent:

import { ShowToastEvent } from 'lightning/platformShowToastEvent';

this.dispatchEvent(
    new ShowToastEvent({
        title: 'Success',
        message: 'Record saved',
        variant: 'success'
    })
);

Official LWC Toast Documentation


65. How do you work with events in Lightning Web Components?

Answer:

In LWC, events are used for communication between components. You can create custom events or use standard events like click or change. Components can communicate upwards (parent to child) or downwards (child to parent) in the component hierarchy.

Example of dispatching a custom event:

const customEvent = new CustomEvent('customeventname', {
    detail: { payload },
    bubbles: true,
    composed: true
});
this.dispatchEvent(customEvent);

Official LWC Event Handling Documentation


66. How do you handle data binding in Lightning Web Components?

Answer:

Data binding in LWC is achieved using reactive properties. When a property’s value changes, the component re-renders automatically.

Example:

// Define a reactive property
@api message = 'Hello';

// Change the property's value
this.message = 'World';

Official LWC Reactive Property Documentation


67. How do you work with wire adapters in Lightning Web Components?

Answer:

Wire adapters in LWC are used to retrieve data from Salesforce. You can use standard wire adapters like getRecord or create custom wire adapters.

Example using getRecord:

import { getRecord } from 'lightning/uiRecordApi';

@wire(getRecord, { recordId: '$recordId', fields: FIELDS })
account;

Official LWC Wire Adapters Documentation


68. How do you implement a modal or popup in a Lightning Web Component?

Answer:

You can implement a modal or popup in LWC by conditionally rendering a hidden or visible component using CSS classes or JavaScript logic.

Example:

<template if:true={isModalOpen}>
    <div class="modal">
        <!-- Modal content goes here -->
    </div>
</template>

MDN Web Docs on Modals


69. How do you work with third-party libraries in Lightning Web Components?

Answer:

You can use third-party libraries in LWC by importing them into your component and using them as needed. Ensure that the library is compatible with LWC and follows Salesforce security policies.

Example:

import externalLibrary from '@salesforce/resourceUrl/externalLibrary';

// Load the library
loadScript(this, externalLibrary + '/library.js')
    .then(() => {
        // Use the library
    })
    .catch(error => {
        // Handle the error
    });

Official LWC Static Resource Documentation


70. How do you handle form validation in a Lightning Web Component?

Answer:

Form validation in LWC can be done using JavaScript and HTML5 form validation attributes like required and pattern. You can also use custom JavaScript validation logic.

Example using HTML5 attributes:

<input type="text" required pattern="[A-Za-z]+" />

MDN Web Docs on Form Validation


71. How do you implement server-side sorting in a Lightning Web Component?

Answer:

Server-side sorting in LWC involves making a request to the server with sorting parameters and processing the data on the server before sending it back to the component.

Example:

// Call server to get sorted data
getSortedData({ sortBy, sortOrder })
    .then(result => {
        // Process the sorted result
    })
    .catch(error => {
        // Handle the error
    });

72. How do you implement dynamic component creation in a Lightning Web Component?

Answer:

Dynamic component creation in LWC is achieved by importing the component’s module and using JavaScript to create and render instances of the component.

Example:

import dynamicComponent from 'c/dynamicComponent';

const element = document.createElement('c-dynamic-component');
element.setAttribute('message', 'Dynamic Component Message');
document.body.appendChild(element);

73. How do you implement a data table with pagination and sorting in a Lightning Web Component?

Answer:

To implement a data table with pagination and sorting in LWC, you can combine server-side pagination and sorting techniques with client-side rendering for a seamless user experience.

Example:

// Call server to get paginated and sorted data
getPaginatedAndSortedData({ pageNumber, pageSize, sortBy, sortOrder })
    .then(result => {
        // Process the paginated and sorted result
    })
    .catch(error => {
        // Handle the error
    });

74. How do you optimize performance in a Lightning Web Component?

Answer:

To optimize performance in LWC, you can follow best practices like minimizing the use of reactive properties, avoiding unnecessary DOM manipulation, and leveraging caching mechanisms.

Example:

// Avoid excessive reactivity
// Bad: this.message = 'New Message';
// Better: this.privateMessage = 'New Message';

// Minimize DOM manipulation
// Bad: this.template.querySelector('input').value = 'New Value';
// Better: this.privateValue = 'New Value';

Official LWC Performance Best Practices


75. How do you handle user authentication and authorization in a Lightning Web Component?

Answer:

User authentication and authorization in LWC are typically handled on the server-side using Salesforce’s authentication and authorization mechanisms. The component can then interact with server resources based on the user’s permissions.

Example:

// Call server to check user's permissions
checkUserPermissions()
    .then(result => {
        // Process the result
    })
    .catch(error => {
        // Handle the error
    });

Official Salesforce Authentication Documentation


76. How do you handle client-side caching in a Lightning Web Component?

Answer:

Client-side caching in LWC involves storing frequently accessed data in memory to reduce the need for repeated server requests. This can be achieved using JavaScript objects or browser storage mechanisms like localStorage or sessionStorage.

Example using localStorage:

// Store data in localStorage
localStorage.setItem('cachedData', JSON.stringify(data));

// Retrieve data from localStorage
const cachedData = JSON.parse(localStorage.getItem('cachedData'));

MDN Web Docs on Web Storage


77. How do you implement lazy loading of images in a Lightning Web Component?

Answer:

Lazy loading of images in LWC involves loading images only when they are in the viewport. This can be achieved using the IntersectionObserver API or by using a third-party library.

Example using IntersectionObserver:

connectedCallback() {
    const observer = new IntersectionObserver(entries => {
        entries.forEach(entry => {
            if (entry.isIntersecting) {
                const image = entry.target;
                const src = image.dataset.src;
                image.src = src;
                observer.unobserve(image);
            }
        });
    });

    this.template.querySelectorAll('img[data-src]').forEach(img => {
        observer.observe(img);
    });
}

MDN Web Docs on Intersection Observer


78. How do you implement client-side routing in a Lightning Web Component?

Answer:

Client-side routing in LWC involves using a routing library like lightning-navigation or a custom router to manage navigation within the application without a full page refresh.

Example using lightning-navigation:

import { NavigationMixin } from 'lightning/navigation';

// Navigate to a page
this[NavigationMixin.Navigate]({
    type: 'standard__webPage',
    attributes: {
        url: '/my-custom-page'
    }
});

Official LWC NavigationMixin Documentation


79. How do you handle errors and exceptions in a Lightning Web Component?

Answer:

Errors and exceptions in LWC can be handled using try-catch blocks or by using error boundaries to catch and display error messages to users.

Example using try-catch:

try {
    // Code that might throw an error
} catch(error) {
    // Handle the error
    console.error(error.message);
}

MDN Web Docs on Error Handling


80. How do you implement infinite scrolling in a Lightning Web Component?

Answer:

Infinite scrolling in LWC involves dynamically loading content as the user scrolls down the page. This can be achieved by detecting scroll events and making requests for additional data.

Example:

window.addEventListener('scroll', () => {
    if (window.innerHeight + window.scrollY >= document.body.offsetHeight) {
        // Load more data
    }
});

MDN Web Docs on Infinite Scrolling


81. How do you integrate a Lightning Web Component with an Aura Component?

Answer:

To integrate an LWC with an Aura Component, you can use the lightning:container or lightning:isUrlAddressable interface. This allows you to embed an LWC within an Aura Component.

Example using lightning:container:

<aura:component>
    <lightning:container aura:id="lwcContainer" src="{!$Resource/lwcBundle}" onmessage="{!c.handleMessage}" />
</aura:component>

Official Salesforce Documentation on LWC Integration with Aura


82. How do you handle concurrent updates in a Lightning Web Component?

Answer:

To handle concurrent updates in LWC, you can use record locking mechanisms like optimistic concurrency control (OCC) or implement custom logic to prevent conflicting updates.

Example using OCC:

// Retrieve the latest version of the record
getRecord({ recordId, fields })
    .then(record => {
        // Compare versions and update if no conflict
    })
    .catch(error => {
        // Handle the error
    });

Official Salesforce Documentation on OCC


83. How do you implement drag and drop functionality in a Lightning Web Component?

Answer:

Implementing drag and drop in LWC involves using HTML5 drag and drop events along with JavaScript to handle the drag and drop operations.

Example:

handleDragStart(event) {
    event.dataTransfer.setData('text/plain', event.target.id);
}

handleDrop(event) {
    event.preventDefault();
    const data = event.dataTransfer.getData('text/plain');
    const draggedElement = document.getElementById(data);
    event.target.appendChild(draggedElement);
}

MDN Web Docs on Drag and Drop


84. How do you integrate a Lightning Web Component with external APIs?

Answer:

To integrate an LWC with external APIs, you can use JavaScript’s fetch API or the XMLHttpRequest object to make HTTP requests to the external endpoint.

Example using fetch:

fetch('https://api.example.com/data')
    .then(response => response.json())
    .then(data => {
        // Process the data from the API
    })
    .catch(error => {
        // Handle the error
    });

MDN Web Docs on Fetch API


85. How do you implement real-time updates in a Lightning Web Component?

Answer:

Real-time updates in LWC can be implemented using technologies like WebSockets or a platform-specific real-time messaging service.

Example using WebSockets:

const socket = new WebSocket('wss://example.com/socket');

socket.addEventListener('message', event => {
    const data = JSON.parse(event.data);
    // Process real-time data
});

MDN Web Docs on WebSockets


86. How do you handle event communication between sibling components in a Lightning Web Component?

Answer:

To handle event communication between sibling components in LWC, you can use a shared parent component as a mediator, or leverage the LightningElement‘s event mechanism for custom events.

Example using a shared parent component:

<!-- Parent Component -->
<template>
    <c-child-component-a oncustomevent={handleCustomEvent}></c-child-component-a>
    <c-child-component-b oncustomevent={handleCustomEvent}></c-child-component-b>
</template>

Official Salesforce Documentation on Event Communication


87. How do you dynamically load JavaScript or CSS resources in a Lightning Web Component?

Answer:

To dynamically load JavaScript or CSS resources in LWC, you can use the loadScript and loadStyle functions from the lightning/platformResourceLoader module.

Example:

import { loadScript, loadStyle } from 'lightning/platformResourceLoader';
import CUSTOM_SCRIPT from '@salesforce/resourceUrl/customScript';
import CUSTOM_STYLE from '@salesforce/resourceUrl/customStyle';

loadScript(this, CUSTOM_SCRIPT)
    .then(() => {
        // Script loaded successfully
    })
    .catch(error => {
        // Handle the error
    });

loadStyle(this, CUSTOM_STYLE)
    .then(() => {
        // Style loaded successfully
    })
    .catch(error => {
        // Handle the error
    });

Official Salesforce Documentation on Resource Loader


88. How do you handle internationalization (i18n) in a Lightning Web Component?

Answer:

To handle internationalization in LWC, you can use the Intl object for date, time, and number formatting, and leverage custom labels for text translations.

Example using Intl object:

const formatter = new Intl.DateTimeFormat('en-US', { year: 'numeric', month: 'long', day: 'numeric' });
const formattedDate = formatter.format(new Date());

MDN Web Docs on Intl

Official Salesforce Documentation on Custom Labels


89. How do you implement dynamic component creation based on user input in a Lightning Web Component?

Answer:

Dynamic component creation based on user input in LWC involves using conditional rendering and JavaScript to instantiate components dynamically.

Example:

// Dynamically instantiate a component
const element = document.createElement('c-dynamic-component');
element.setAttribute('message', 'Dynamic Component Message');
document.body.appendChild(element);

90. How do you implement data binding in a Lightning Web Component?

Answer:

Data binding in LWC is achieved using reactive properties and getters/setters to update the UI in response to changes in data.

Example:

// Reactive property
@track message = 'Hello World';

// Getter and setter
get formattedMessage() {
    return this.message.toUpperCase();
}

set formattedMessage(value) {
    this.message = value.toLowerCase();
}

Official Salesforce Documentation on Data Binding


91. How do you work with form elements and handle form submission in a Lightning Web Component?

Answer:

Working with form elements in LWC involves using standard HTML form elements and handling their events like submit and change.

Example:

<template>
    <lightning-input label="Name" value={name} onchange={handleChange}></lightning-input>
    <lightning-button label="Submit" onclick={handleSubmit}></lightning-button>
</template>
// Handle change event
handleChange(event) {
    this.name = event.target.value;
}

// Handle form submission
handleSubmit() {
    // Perform form submission logic
}

Official Salesforce Documentation on Lightning Input


92. How do you implement client-side caching in a Lightning Web Component?

Answer:

Client-side caching in LWC can be achieved using browser storage mechanisms like localStorage or sessionStorage to store and retrieve data.

Example using localStorage:

// Save data to local storage
localStorage.setItem('key', 'value');

// Retrieve data from local storage
const data = localStorage.getItem('key');

MDN Web Docs on Web Storage


93. How do you handle errors and exceptions in a Lightning Web Component?

Answer:

Handling errors and exceptions in LWC involves using try-catch blocks to gracefully handle potential exceptions.

Example:

try {
    // Code that may throw an error
} catch (error) {
    // Handle the error
    console.error(error.message);
}

94. How do you perform unit testing for a Lightning Web Component?

Answer:

Unit testing for LWC can be done using Jest and the @salesforce/sfdx-lwc-jest library provided by Salesforce.

Example unit test:

import { createElement } from 'lwc';
import MyComponent from 'c/myComponent';

describe('c-my-component', () => {
    it('renders correctly', () => {
        const element = createElement('c-my-component', {
            is: MyComponent
        });
        document.body.appendChild(element);
        expect(element.shadowRoot.querySelector('p').textContent).toBe('Hello World');
    });
});

Official Salesforce Documentation on LWC Testing


95. How do you implement pagination in a Lightning Web Component?

Answer:

Implementing pagination in LWC involves using variables to track the current page and a method to update the displayed data based on the selected page.

Example:

// HTML
<lightning-button label="Next" onclick={handleNext}></lightning-button>

// JavaScript
handleNext() {
    this.currentPage++;
    this.updateDisplayedData();
}

96. How do you implement lazy loading of images in a Lightning Web Component?

Answer:

Lazy loading of images in LWC can be achieved using the Intersection Observer API to only load images when they are in the viewport.

Example:

// JavaScript
connectedCallback() {
    const observer = new IntersectionObserver(entries => {
        entries.forEach(entry => {
            if (entry.isIntersecting) {
                const image = entry.target;
                image.src = image.dataset.src;
                observer.unobserve(image);
            }
        });
    });

    observer.observe(this.template.querySelector('img'));
}

// HTML
<img data-src="image-url.jpg" alt="Lazy Loaded Image">

MDN Web Docs on Intersection Observer API


97. How do you implement client-side routing in a Lightning Web Component?

Answer:

Client-side routing in LWC can be achieved using the lightning-navigation service to navigate between different pages without a full page refresh.

Example:

import { NavigationMixin } from 'lightning/navigation';

// Navigate to a record page
this[NavigationMixin.Navigate]({
    type: 'standard__recordPage',
    attributes: {
        recordId: '001XXXXXXXXXXXXXXX',
        objectApiName: 'Account',
        actionName: 'view'
    }
});

Official Salesforce Documentation on Navigation


98. How do you handle large lists or data sets efficiently in a Lightning Web Component?

Answer:

Handling large lists or data sets in LWC involves using pagination, lazy loading, or implementing virtual scrolling to only load and display a subset of the data at a time.

Example using pagination:

handleNext() {
    this.currentPage++;
    this.updateDisplayedData();
}

99. How do you integrate external libraries or frameworks with a Lightning Web Component?

Answer:

Integrating external libraries or frameworks in LWC can be done by importing and using them in the component.

Example with D3.js library:

import { loadScript } from 'lightning/platformResourceLoader';
import D3 from '@salesforce/resourceUrl/d3';

loadScript(this, D3)
    .then(() => {
        // D3.js is now available for use
        const svg = d3.select('body').append('svg');
    })
    .catch(error => {
        // Handle the error
    });

100. How do you optimize performance in a Lightning Web Component?

Answer:

Optimizing performance in LWC involves techniques like minimizing the use of reactive properties, avoiding unnecessary re-renders, and leveraging asynchronous operations for long-running tasks.

Example using @track:

// Inefficient, triggers re-render on every property change
@track data = [];

// More efficient, only re-renders when data reference changes
data = [...this.data, newItem];

Official Salesforce Documentation on Performance Best Practices