LWC Interview: Top Questions and Answers

As a developer, the ability to work with the Lightning Web Component (LWC) framework is becoming increasingly important. This is why many companies are looking for experienced LWC developers to join their teams. If you’re preparing for an LWC interview, you’ll want to be ready to answer a variety of questions. In this blog post, we’ll take a look at the top LWC interview questions and provide detailed answers to help you prepare.

First, let’s define what the Lightning Web Component (LWC) framework is. LWC is a new programming model for building Lightning components on the Salesforce platform. Lightning Web Components is a new programming model for building Lightning components. It uses web standards and provides better performance than the previous model, Aura. LWC is lightweight, fast, and easy to use. It is built on web standards, which means you can use any JavaScript library or framework.

The questions in this post cover a wide range of topics, from the basics of LWC to more advanced concepts. Whether you’re a beginner or an experienced developer, you’ll find something here to help you prepare for your interview. We’ll start with the basics and move on to more advanced topics. So, let’s dive in!

❶ How would you design and implement a custom Lightning Web Component that utilizes the Salesforce platform’s caching mechanism to improve performance?

One way to design and implement a custom Lightning Web Component that utilizes the Salesforce platform’s caching mechanism to improve performance would be to use the @wire decorator to retrieve data from an Apex class. The @wire decorator automatically caches the data that it retrieves, so that it does not need to be retrieved again unless the data changes or the cache is explicitly invalidated.

Here is an example of a Lightning Web Component that retrieves a list of accounts from an Apex class using the @wire decorator:

import { LightningElement, wire } from 'lwc';
import getAccounts from '@salesforce/apex/AccountController.getAccounts';
export default class AccountList extends LightningElement {
@wire(getAccounts) accounts;
}

In this example, the getAccounts function is an Apex class that retrieves a list of accounts from the Salesforce database. The @wire decorator is used to call the getAccounts function and store the results in the accounts property of the component. The @wire decorator also automatically caches the results of the getAccounts function, so that they do not need to be retrieved again unless the data changes or the cache is explicitly invalidated.

To display the list of accounts in the component’s template, you can use a template for:each to iterate over the accounts.data property and display each account.

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

In this example, the template for:each iterates over the accounts.data property and displays the name of each account. The key attribute on the p element is used to set a unique key for each account, which can improve the performance of the component.

It’s also worth mentioning that the @wire decorator can be used with the refreshApex method to refresh the cache, this method accepts a parameter this.accounts.data, this way the component will retrieve the data again and update the component.

import { refreshApex } from '@salesforce/apex';

refreshApex(this.accounts.data);

This approach will improve the performance of the component by reducing the number of calls to the server and by reducing the amount of data that needs to be sent over the network.

❷ Can you explain the difference between a Lightning Web Component’s public and private properties, and provide an example of when you would use each?

In a Lightning Web Component, properties can be defined as either public or private. The main difference between public and private properties is the accessibility and scope of the properties.

  • Public properties: Public properties are defined by annotating them with the @api decorator. These properties are accessible from both the JavaScript class and the template of the component. They can also be accessed by other components that use this component. Public properties can be passed as attributes to the component and can also be used as event payloads.

import { LightningElement, api } from 'lwc';
export default class MyComponent extends LightningElement {
@api message = 'Hello, World!';
}

<template>
<p>{message}</p>
</template>
view raw template.html hosted with ❤ by GitHub

  • Private properties: Private properties, on the other hand, are not annotated with the @api decorator. These properties are only accessible from the JavaScript class of the component and not from the template. They are also not accessible by other components that use this component.

import { LightningElement } from 'lwc';
export default class MyComponent extends LightningElement {
_secret = 'This is a secret message';
get secretMessage() {
return this._secret;
}
}

You should use public properties when you want to make data accessible to both the template and other components. For example, when you want to pass data to a child component or when you want to display data on the template.

You should use private properties when you want to store data that should only be accessible within the component’s JavaScript class. For example, when you want to store data that is only used to calculate other properties or when you want to store data that is not intended to be displayed on the template.

Also, it’s worth mentioning that in some cases, you may want to keep a property private, and only expose it through a getter method or setter, this way you can control how and when that property is read or modified.

❸ How do you handle data binding and communication between Lightning Web Components?

One of the key features of Lightning Web Components is the ability to bind data between different components. This allows for the seamless flow of data and communication between different parts of an application.

Data binding in Lightning Web Components is achieved through the use of properties and events. Properties are used to define the data that is passed between components, while events are used to trigger changes in the properties.

For example, let’s say we have a parent component that displays a list of contacts and a child component that displays the details of a specific contact. The parent component would use a property to pass the selected contact to the child component, which would then display the details of that contact.

The parent component would also use an event to notify the child component when the selected contact has changed. The child component would then update its data accordingly.

This is just one example of how data binding and communication can be used in Lightning Web Components. Other examples include passing data between related components, or between different levels of a component hierarchy. The key is to use properties and events to define the data that is being passed and the actions that are being taken, which will make it easy to manage and maintain your application.

❹ Can you give an example of how you have used the Lightning Data Service in a Lightning Web Component?

Here is an example of how I have used the Lightning Data Service (LDS) in a Lightning Web Component:

I was working on a project where I needed to display a form for creating new Accounts. I used the Lightning Data Service to handle the form data and create the new Account record.

Here is an example of the component’s HTML template:

<template>
<lightning-record-form object-api-name="Account"
layout-type="Full"
columns="2"
mode="edit"
onsuccess={handleSuccess}>
</lightning-record-form>
</template>

And here is an example of the component’s JavaScript controller:

import { LightningElement } from 'lwc';
export default class CreateAccount extends LightningElement {
handleSuccess(event) {
// Account record has been created
// You can get the recordId from the event.detail.id
const recordId = event.detail.id;
console.log('New Account created with Id: ' + recordId);
}
}
view raw ldsComponent.js hosted with ❤ by GitHub

As you can see, I used the lightning-record-form component to display the form and the object-api-name attribute to specify that I am working with the Account object. The mode attribute is set to “edit” so that the form will be used for creating a new record.

The onsuccess attribute is used to handle the success event, and it will fire when the form is submitted and the new Account record is created. In this example, I used the handleSuccess function which is called when the form is submitted, and it will log the newly created record’s ID.

By using the Lightning Data Service, I was able to handle the form data and create the new Account record with just a few lines of code, without having to write any Apex controllers or custom logic. This made the development process much easier and more efficient.

Additionally, Lightning Data Service automatically handles the security and sharing rules, so that the data is only accessible to authorized users, which makes the development process more secure.

❺ Can you explain the use of slots and how they can be used to create reusable components?

Slots in Lightning Web Components (LWC) are a mechanism for component composition, allowing developers to create reusable components that can be nested and reused within other components.

A component can define one or more slots, which act as placeholders for other components to be inserted. The component that inserts the child component into the slot is called the parent component, and the component that is inserted into the slot is called the child component.

Here is an example of a parent component that defines a slot:

<template>
<div class="parent">
<div class="header">
<slot name="header"></slot>
</div>
<div class="body">
<slot name="body"></slot>
</div>
<div class="footer">
<slot name="footer"></slot>
</div>
</div>
</template>
view raw slot.html hosted with ❤ by GitHub

In this example, the parent component defines three slots with the names “header”, “body”, and “footer”. These slots can be used to insert child components in the corresponding areas of the parent component.

Here is an example of a child component that can be inserted into the parent component’s slots:

<template>
    <div class="child">
        <h1>Child Title</h1>
        <p>Child Content</p>
    </div>
</template>

This child component can be inserted into the parent component’s “header” slot like this:

<parent-component>
    <div slot="header">
        <child-component></child-component>
    </div>
</parent-component>

By using slots, the parent component can define a structure and layout for child components, without specifying the content of the child components. This allows for great flexibility and reusability, as the same parent component can be used with different child components, or the same child component can be used in different parent components.

Additionally, slots also support fallback content

❻ How do you handle server-side data validation in a Lightning Web Component?

Handling server-side data validation in a Lightning Web Component can be done using Apex controllers. The Apex controller can be used to perform the validation and return the results back to the Lightning Web Component.

Firstly, I would create a custom Apex class that will handle the validation logic. This class would have methods that take in the data from the component and perform the necessary validation checks. For example, if a field is required, the method would check if the field is empty and return an error message if it is.

Once the validation logic is in place, I would then create a Lightning Web Component that calls the Apex class methods to perform the validation. The component would have input fields that the user can interact with, and when the user submits the form, the component would call the Apex methods and pass in the data from the input fields.

The Apex methods would then perform the validation and return the results back to the component. The component would then display any errors to the user if there are any, or if the data is valid, it would proceed with the next step in the process.

It’s also worth noting that, we can also use lightning-input-field component to handle the input validation automatically and we don’t need to use Apex for that.

Overall, the key to handling server-side data validation in a Lightning Web Component is to use an Apex controller to perform the validation and return the results back to the component. The component can then display any errors to the user, or proceed with the next step in the process if the data is valid.

Here is a sample of an example of how server-side data validation can be implemented in a Lightning Web Component using an Apex controller:

Apex Controller:

public with sharing class ValidationController {
@AuraEnabled
public static ValidationResult validateData(String name, String email, Integer age) {
ValidationResult result = new ValidationResult();
if (name == null || name.isEmpty()) {
result.addError('Name is required');
}
if (email == null || email.isEmpty() || !email.contains('@')) {
result.addError('Valid email is required');
}
if (age == null || age < 18) {
result.addError('Age must be 18 or older');
}
return result;
}
public class ValidationResult {
@AuraEnabled
public List<String> errors { get; set; }
public ValidationResult() {
errors = new List<String>();
}
public void addError(String error) {
errors.add(error);
}
}
}

Lightning Web Component JS:

import { LightningElement, track, wire } from 'lwc';
import validateData from '@salesforce/apex/ValidationController.validateData';
export default class MyComponent extends LightningElement {
@track name;
@track email;
@track age;
@track errors = [];
handleSubmit() {
validateData({ name: this.name, email: this.email, age: this.age })
.then(result => {
if (result.errors.length > 0) {
this.errors = result.errors;
} else {
// proceed with next step in process
}
})
.catch(error => {
console.error(error);
});
}
}
view raw validate.js hosted with ❤ by GitHub

In this example, the Apex controller has a method called “validateData” that takes in 3 parameters – “name”, “email”, and “age”. The method performs validation checks on each of these inputs and returns a “ValidationResult” object that contains any errors that were found.

In the Lightning Web Component, the “handleSubmit” method is called when the user submits the form. It calls the “validateData” Apex method and passes in the data from the input fields. The method then checks the result for any errors. If there are any errors, it sets the “errors” track property to the list of errors returned by the Apex method, which can then be displayed to the user. If there are no errors, it proceeds with the next step in the process.

This is just one example of how server-side data validation can be implemented in a Lightning Web Component. It can be adjusted to fit the specific needs of the application and validation requirements.

❼ Can you explain how you would implement a nested component hierarchy in a Lightning Web Component?

Implementing a nested component hierarchy in a Lightning Web Component involves creating child components that are used within the parent component. The child components can be used to encapsulate specific functionality and can be reused throughout the application.

Here is an example of how a nested component hierarchy can be implemented:

  1. Create the child components: The first step is to create the child components that will be used within the parent component. These components can be created using the Lightning Web Component CLI or by manually creating the necessary files. Each child component should have its own HTML, JS, and CSS files.
  2. Define the parent component: Next, create the parent component that will use the child components. The parent component should have its own HTML, JS, and CSS files. In the HTML file, use the <template> tag to include the child components within the parent component.
  3. Pass data between components: To pass data between the parent and child components, you can use the @api decorator in the child component’s JS file. The parent component can then pass data to the child component using the child-component-name attribute in the HTML file.
  4. Handle events: To handle events between the parent and child components, you can use the @track decorator in the child component’s JS file. The child component can then use the dispatchEvent method to send events to the parent component, which can then handle the event using the addEventListener method.
  5. Use the parent component: Finally, use the parent component in your application. The parent component will include the child components and pass data between them as needed. The parent component can also handle events from the child components.

By implementing a nested component hierarchy, we can encapsulate specific functionality within the child components, making the parent component more readable and easier to maintain. The child components can also be reused throughout the application, reducing the amount of code needed to be written and maintain.

❽ How do you ensure the performance and scalability of a Lightning Web Component in a large-scale Salesforce org?

To ensure the performance and scalability of a Lightning Web Component in a large-scale Salesforce org, I would take the following steps:

  1. Minimize the use of Apex controllers and rely on client-side logic as much as possible to reduce server load.
  2. Optimize the component’s data loading and rendering by using lazy loading, pagination, and caching techniques.
  3. Utilize the Salesforce Performance Resource Bundle to reduce the number of network requests and improve the loading speed of the component.
  4. Test the component’s performance in a large data set to identify and fix any performance bottlenecks.
  5. Use the Salesforce Lightning Locker service to isolate the component’s code and data from other components and protect against cross-site scripting attacks.
  6. Ensure the code is clean, efficient, and follows best practices.
  7. Monitor the component’s performance regularly and make adjustments as necessary.

It is also important to be mindful of performance considerations during the design phase and to make sure that the component is designed to handle large data sets and a large number of users.

❾ How do you handle data validation and error handling in a Lightning Web Component?

Handling data validation and error handling in a Lightning Web Component can be accomplished through a combination of client-side and server-side logic.

  1. On the client-side, I would use JavaScript and HTML5 form validation to ensure that the data entered by the user meets certain criteria, such as being a required field or having a specific format. I would also use custom validation functions to check for specific business rules that are not covered by HTML5 validation.
  2. On the server-side, I would use Apex controllers to validate the data once it is submitted by the user, and to ensure that the data is consistent with the data stored in the Salesforce org. I would also use Apex exceptions to handle any errors that occur during the validation process.
  3. To present the error messages to the user, I would use toast notifications to show the error message and prompt the user to correct the issue. I would also use the lightning-output-field component to show the error messages next to the fields where the user input is incorrect.
  4. I would also consider implementing a global error handling mechanism that can handle errors that are thrown by all the components in the app, this can be done by implementing a global error handler that listens to the errors that are thrown by the components and handles them accordingly.

❶ 𝟬 How do you work with data models and data controllers in a complex Lightning Web Component, and what are some of the best practices for managing data and state?

Working with data models and data controllers in a complex Lightning Web Component involves designing and implementing a structured approach to managing the data and state of the component. This includes defining the data model and data structure, as well as the various data controllers that will be responsible for managing the data and state of the component.

One of the key best practices for managing data and state in a complex Lightning Web Component is to use a modular and reusable data model. This allows for easy management and manipulation of the data and state, as well as the ability to easily update or modify the data model as needed.

Another best practice is to use a centralized data controller that is responsible for managing the data and state of the component. This allows for easy access to the data and state throughout the component, as well as the ability to easily update or modify the data as needed.

Additionally, it is important to use efficient data binding techniques to ensure that the data is updated and displayed correctly in the component. This includes using two-way data binding and event handling to ensure that the data and state are always in sync with the component.

Finally, it is important to use best practices for data security, such as data validation and data sanitation, to ensure that the data is safe and secure. This includes using secure data storage and encryption to protect sensitive data, as well as using data validation techniques to ensure that the data is valid and consistent.

In conclusion, the LWC framework is a powerful tool for building lightning components on the Salesforce platform. As a developer, being proficient in this framework is becoming increasingly important. By preparing for the top LWC interview questions, you’ll be able to confidently demonstrate your skills and knowledge to potential employers. We hope that this blog post has provided you with the information and resources you need to succeed in your LWC interview. Remember to practice and stay up-to-date on the latest developments in the LWC framework. Best of luck in your interview and your career in LWC development!

About the blog

SFDCLessons is a blog where you can find various Salesforce tutorials and tips that we have written to help beginners and experienced developers alike. we also share my experience and knowledge on Salesforce best practices, troubleshooting, and optimization. Don’t forget to follow us on:

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