LWC Interview Questions: Series 1

(2024)

Lightning Web Components (LWC) are a potent tool for developing dynamic and responsive user interfaces in the field of Salesforce development. Because of its capacity to provide improved performance and a more efficient development process, LWC is now a fundamental component of contemporary Salesforce platform apps. Finding qualified LWC developers is essential for managers and interviewers to put up a competent team that can fully utilize this technology.

We’ve compiled a thorough collection of LWC interview questions that address conceptual understanding and real-life scenarios to help with this effort. The purpose of these questions is to evaluate a candidate’s problem-solving abilities, expertise with LWC development, and application of best practices in Salesforce development. Now let’s get started!

MIND IT !

Preparing for an LWC interview can be an overwhelming task. It requires a solid understanding of LWC concepts, best practices, and hands-on experience. To help you in your journey, we have curated a comprehensive list of interview questions that cover a wide range of topics related to LWC.

In this blog series, I have tried to cover all conceptual and scenario-based LWC Interview Questions that LWC Developers often ask in an interview.

Interview Series

Let’s start the interview series on Lightning Web Components (Between Interviewer & Interviewee).

Conceptual Questions:

Interviewer: What are Lightning Web Components (LWC), and how do they differ from Aura components?

Interviewee:

Lightning Web Components (LWC) are a new programming model for building Lightning components on the Salesforce platform. They leverage modern web standards like ECMAScript 6 and provide better performance compared to Aura components. Unlike Aura, LWC uses a more lightweight framework and promotes a simpler, standards-based approach to web development.

MIND IT !

Here the interviewer can also ask the above questions in another way.

Interviewer: What are the key differences between LWC and Aura components? Compare their architecture, performance, and development experience.

Interviewee: Differences Between LWC and Aura Components:

1. Architecture:

Aura Components:

• Based on the Aura framework, which utilizes a client-side JavaScript framework and a server-side Apex controller.
• Follows a component-based architecture with markup, JavaScript controller, and style encapsulated within a single file.
• Utilizes the Aura component model for communication between components, including events, attributes, and methods.

LWC (Lightning Web Components):

• Based on web standards and built on top of modern web components standards supported by the W3C.
• Follows a modular architecture with separate files for markup, JavaScript, and style, adhering to the Shadow DOM for encapsulation.
• Utilizes ECMAScript modules and standard DOM APIs for component development, providing better interoperability with other frameworks.

2. Performance:

Aura Components:

• Performance can be impacted by the framework’s overhead and the use of the Aura component model for communication.
• Server round-trips for data retrieval and updates can introduce latency and affect overall performance.

LWC (Lightning Web Components):

• Offers improved performance due to the use of native web standards and optimizations such as Shadow DOM and Virtual DOM.
• Client-side rendering and minimal server round-trips contribute to faster loading times and better responsiveness.

3. Development Experience:

Aura Components:

• Development experience can be characterized by the Aura framework’s learning curve and complexity.
• Requires familiarity with Aura-specific concepts such as controllers, helpers, and events.
• Tooling support for Aura development may be more limited compared to other modern web development frameworks.

LWC (Lightning Web Components):

• Offers a more streamlined and modern development experience with support for ECMAScript 6+ features and standard web APIs.
• Leverages modern tooling such as the Salesforce CLI and VS Code extensions for efficient development workflows.
• Provides a cleaner and more intuitive syntax compared to Aura, resulting in improved readability and maintainability of code.

Summary: Overall, LWC represents a significant evolution from Aura Components, offering a more modern and performance-oriented approach to building components on the Salesforce platform. While Aura Components continue to be supported, LWC is positioned as the future direction for Salesforce development, offering developers a more efficient and scalable framework for building Lightning UIs.

Interviewer: Explain the concept of data binding in LWC. How does it facilitate communication between a component’s JavaScript controller and its HTML template?

Interviewee:

Data binding in Lightning Web Components (LWC) is a mechanism that establishes a connection between a component’s JavaScript controller and its HTML template. It enables the synchronization of data between the two, ensuring that any changes made in the JavaScript controller are reflected in the HTML template, and vice versa. Data binding facilitates seamless communication and interaction within the component, allowing for dynamic updates and rendering of content based on changes in data or user input.

In simple words when you map your data from the backend(JS) to the front end(HTML) that’s called data binding in LWC.

How Data Binding Facilitates Communication:

1. Property Binding:

• Property binding allows for the binding of JavaScript properties to elements or attributes in the HTML template.
• It uses the curly brace syntax `{}` to reference JavaScript properties within the HTML template.
• When a property value changes in the JavaScript controller, the corresponding element or attribute in the HTML template is automatically updated to reflect the new value.
• Similarly, changes made to the value in the HTML template are reflected back to the JavaScript controller.

2. Event Binding:

• Event binding enables the binding of DOM events to methods or functions in the JavaScript controller.
• It uses the `on-` prefix followed by the name of the event to specify event binding in the HTML template.
• When the specified DOM event is triggered, the associated method or function in the JavaScript controller is invoked.
• This allows for the handling of user interactions or browser events within the component’s logic.

Here’s an example demonstrating data binding in LWC:

HTML Template (dataBinding.html):

<!--dataBinding.html-->
<template>
  <lightning-card title="Input Component Example" variant="narrow">
    <div class="slds-p-around_medium">
      <p>{message}</p>
      <div class="slds-m-top_medium">
        <lightning-input type="text" onchange={handleChange}></lightning-input>
      </div>
    </div>
  </lightning-card>
</template>

JavaScript Controller (dataBinding.js):

//dataBinding.js
import { LightningElement,track } from 'lwc';
 
export default class DataBinding extends LightningElement {
  @track message = 'Initial message';
 
  handleChange(event) {
      this.message = event.target.value;
  }
}

In this example:

• The `{message}` syntax in the HTML template represents property binding, where the `message` property in the JavaScript controller is bound to the content of the `<p>` element.
• When the value of the input field changes (`onchange` event), the `handleChange` method in the JavaScript controller is called, updating the `message` property.

As a result, the content of the `<p>` element is automatically updated to reflect the new value of the `message` property.

Output:

Overall, data binding in LWC facilitates seamless communication between a component’s JavaScript controller and its HTML template, enabling dynamic updates and interaction within the component’s UI.

Interviewer: What is the Shadow DOM, and how does LWC utilize it?

Interviewee:

The Shadow DOM (Shadow Document Object Model) is a fundamental feature of web components that allows encapsulation of styles, markup, and behavior within a scoped boundary, separate from the rest of the document. This encapsulation prevents styles and scripts from leaking out and conflicting with other parts of the page, thus providing better modularity and reusability.

In Lightning Web Components (LWC), the Shadow DOM is utilized to isolate the component’s markup and styling from the surrounding document. This means that styles defined within a component only apply to the elements within that component’s Shadow DOM, preventing unintended styling conflicts with other components or elements on the page.

Example:

Consider a simple LWC component named helloWorld that displays a greeting message:

<!-- helloWorld.html -->
<template>
    <div class="container">
        <h1>{greeting}</h1>
    </div>
</template>

// helloWorld.js
import { LightningElement } from 'lwc';
 
export default class HelloWorld extends LightningElement {
    greeting = 'Hello, World!';
}

In this example:

• The `helloWorld` component consists of a `<div>` container with a `<h1>` heading displaying the value of the `greeting` property.
• The `greeting` property is defined in the JavaScript file and initialized with the value “Hello, World!”.

Output:

When the `helloWorld` component is rendered in a Lightning Web Component context, it generates its own Shadow DOM. The resulting output in the browser would look like this:

<!----shadow-root (open)---->
    <div class="container">
        <h1>Hello, World!</h1>
    </div>
<!----/shadow-root---->

The `<div class=”container”>` and `<h1>` elements are encapsulated within the Shadow DOM boundary of the `helloWorld` component. Any styles applied to these elements will only affect elements within the component, ensuring isolation and preventing unintended styling conflicts.

In summary, the Shadow DOM in LWC provides a mechanism for encapsulating component markup, styling, and behavior, leading to enhanced modularity, reusability, and better encapsulation of component functionality.

Interviewer: Differentiate between imperative and declarative programming in the context of LWC.

Interviewee:

In the context of Lightning Web Components (LWC), imperative and declarative programming represent two distinct approaches to building and interacting with components.

Imperative Programming:

Imperative programming involves specifying detailed instructions that explicitly define how a task should be performed. In the context of LWC, imperative programming typically involves directly manipulating the DOM or making imperative API calls to interact with external resources.

Example of imperative programming in LWC:

import { LightningElement, wire } from 'lwc';
import { getRecord } from 'lightning/uiRecordApi';
 
export default class ImperativeExample extends LightningElement {
    recordId;
    error;
 
    @wire(getRecord, { recordId: '$recordId', fields: ['Account.Name'] })
    wiredRecord({ error, data }) {
        if (data) {
            // Handle data
        } else if (error) {
            // Handle error
        }
    }
 
    handleClick() {
        // Imperative call to load record data
        this.recordId = '001XXXXXXXXXXXXXXX';
    }
}

Declarative Programming:

Declarative programming, on the other hand, involves specifying what should be accomplished without explicitly detailing how it should be done. In LWC, declarative programming often involves defining component behavior using markup and leveraging built-in features and functionalities provided by the framework.

Example of declarative programming in LWC:

<!--declarativeExample.html-->
<template>
    <lightning-card title="Declarative Example">
        <div if:true={isDataLoaded}>
            <!-- Declarative rendering based on data -->
            <p>{accountName}</p>
        </div>
        <div if:true={error}>
            <!-- Declarative rendering based on error -->
            <p>Error: {error}</p>
        </div>
        <lightning-button label="Load Data" onclick={handleClick}></lightning-button>
    </lightning-card>
</template>

//declarativeExample.js
import { LightningElement, wire } from 'lwc';
import { getRecord } from 'lightning/uiRecordApi';
 
export default class DeclarativeExample extends LightningElement {
    recordId = '001XXXXXXXXXXXXXXX';
    error;
    accountName;
    isDataLoaded = false;
 
    @wire(getRecord, { recordId: '$recordId', fields: ['Account.Name'] })
    wiredRecord({ error, data }) {
        if (data) {
            // Declaratively handle data
            this.accountName = data.fields.Name.value;
            this.isDataLoaded = true;
        } else if (error) {
            // Declaratively handle error
            this.error = error.body.message;
        }
    }
 
    handleClick() {
        // Declaratively trigger record data load
        this.recordId = '001XXXXXXXXXXXXXXX';
    }
}

In this example:

• `accountName` and `isDataLoaded` are initialized as component properties.
• The recordId is directly assigned to the property `recordId` in the JavaScript class. This eliminates the need to call `this.recordId = ‘001XXXXXXXXXXXXXXX’;` inside `handleClick()`.
• When the component loads, it automatically fetches the account record’s name using the wire adapter.
• The button click event triggers the record data load, but since you’re using a static recordId, it doesn’t change anything visibly.

Output:

Difference:

The main difference between imperative and declarative programming in LWC lies in how component behavior is defined and implemented:

1. Imperative Programming:

• Involves specifying explicit instructions on how to perform tasks.
• Often involves directly manipulating the DOM or making imperative API calls.
• Offers more control and flexibility but can result in verbose and less readable code.

2. Declarative Programming:

• Involves defining what should be accomplished without specifying how it should be done.
• Often involves defining component behavior using markup and leveraging built-in features provided by the framework.
• Offers a more concise and expressive way of defining component behavior, resulting in cleaner and more maintainable code.

In LWC development, both imperative and declarative programming paradigms have their place, and developers often choose the approach that best suits the specific requirements and complexity of their components.

Interviewer: How does LWC facilitate communication between components?

Interviewee:

LWC provides several mechanisms for component communication, including property passing, event handling, and pub-sub patterns. Components can exchange data through attributes and properties, dispatching and handling events, or by subscribing to custom events using the Lightning message service or platform events.

MIND IT !

Here the interviewer can also ask the above questions in another way.

Interviewer: What are the different ways to communicate between Lightning Web Components? Compare and contrast the usage of component events, public properties, and methods.

Interviewee:

In Lightning Web Components (LWC), there are several ways to facilitate communication between components, each with its own use cases and advantages. The primary methods include component events, public properties, and methods. Let’s compare and contrast these approaches:

1. Component Events:

Purpose: Component events allow communication between components that aren’t directly related in the component hierarchy. They enable loose coupling between components by allowing them to communicate without needing to know each other’s implementation details.

Usage: A component dispatches an event using the `CustomEvent` constructor or the `dispatchEvent` method. Other components can handle these events using event handlers in their templates.

Example:

// Dispatching a custom event
this.dispatchEvent(new CustomEvent('customEventName', { detail: eventData }));

Pros:

• Decouples components, making them more reusable and modular.
• Allows communication between components regardless of their hierarchical relationship.

Cons:

• Requires additional setup and overhead compared to other methods.
• Can be more complex to implement and understand, especially for beginners.

2. Public Properties:

Purpose: Public properties are attributes exposed by a component that can be set or accessed by other components. They enable parent-to-child communication, allowing a parent component to pass data or configuration to its child components.

Usage: Public properties are decorated with the `@api` decorator in the child component. The parent component sets the value of these properties when instantiating the child component.

Example:

// Child component
import { LightningElement, api } from 'lwc';
export default class ChildComponent extends LightningElement {
    @api message;
}

Pros:

• Simple and straightforward to implement.
• Facilitates communication between parent and child components.

Cons:

• Limited to parent-child relationships, restricting its use for more complex communication scenarios.
• Exposes component internals to the parent component, potentially leading to tight coupling.

3. Methods:

Purpose: Methods allow components to expose functionality that can be invoked by other components. They enable both parent-to-child and child-to-parent communication, allowing components to interact and collaborate.

Usage: A method is defined in a component’s JavaScript class and can be invoked by other components via a method call.

Example:

// Child component
import { LightningElement } from 'lwc';
export default class ChildComponent extends LightningElement {
    handleClick() {
        // Handle click logic
    }
}

Pros:

• Provides a way for components to interact and collaborate by invoking each other’s functionality.
• Supports both parent-to-child and child-to-parent communication.

Cons:

• Limited to components that have a reference to each other, restricting its use for more loosely coupled scenarios.
• Can lead to tight coupling if overused or misused.

In summary, component events, public properties, and methods are all valuable tools for facilitating communication between Lightning Web Components. The choice of which method to use depends on the specific requirements of the communication scenario, the relationship between the components involved, and the desired level of encapsulation and coupling.

Interviewer: Explain the concept of lifecycle hooks in LWC. What are the different lifecycle hooks available, and when are they invoked during a component’s lifecycle?

Interviewee:

Lifecycle hooks in Lightning Web Components (LWC) are methods that are automatically invoked at specific points during the lifecycle of a component. These hooks allow developers to execute custom logic at various stages of a component’s lifecycle, such as initialization, rendering, and destruction. By leveraging lifecycle hooks, developers can perform tasks like initializing data, fetching external resources, and cleaning up resources when a component is destroyed.

Different Lifecycle Hooks in LWC:

1. constructor():

• Invoked when a component is created.
• Used for initializing component properties and state.

Example:

constructor() {
    super();
    // Initialization logic
}

2. connectedCallback():

• Invoked when a component is inserted into the DOM.
• Used for performing setup tasks that require access to the DOM.

Example:

connectedCallback() {
    // Setup tasks
}

3. renderedCallback():

• Invoked after a component’s template has been rendered.
• Used for performing actions that depend on the rendered DOM.

Example:

renderedCallback() {
    // DOM manipulation
}

4. disconnectedCallback():

• Invoked when a component is removed from the DOM.
• Used for cleaning up resources or performing cleanup tasks.

Example:

disconnectedCallback() {
    // Cleanup tasks
}

5. render():

• Invoked to render the component’s template.
• Used for defining the structure and content of the component’s UI.

Example:

render() {
    return html`<div>Hello, World!</div>`;
}

6. reconnectedCallback():

• Invoked when a component is reinserted into the DOM after being removed.
• Used for reinitializing state or performing setup tasks.

Example:

reconnectedCallback() {
    // Reinitialization tasks
}

Invocation of Lifecycle Hooks:

• Constructor: Invoked when the component is created.
• Connected Callback: Invoked when the component is inserted into the DOM.
• Rendered Callback: Invoked after the component’s template has been rendered.
• Disconnected Callback: Invoked when the component is removed from the DOM.
• Render: Invoked whenever a component needs to render its template.
• Reconnected Callback: Invoked when the component is reinserted into the DOM after being removed.

By understanding the lifecycle hooks available in LWC and their invocation order, developers can effectively manage component initialization, rendering, and cleanup tasks, ensuring optimal performance and behavior throughout the component’s lifecycle.

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Hopefully, this interview series on Lightning Web Components (LWC) will help to understand LWC Conceptual Questions clearly and crack the interview.

All the Best…!!

Thanks for reading ☺️