Mastering LWC Interview Questions in 2024: A Comprehensive Guide

As the demand for Salesforce developers continues to soar, proficiency in Lightning Web Components (LWC) has become a highly sought-after skill. LWC is a programming model introduced by Salesforce in 2018, designed to create custom HTML elements using HTML and JavaScript. With its increasing popularity, it’s crucial for job seekers and professionals to be well-prepared for LWC interview questions.

In this comprehensive guide, we’ll dive into the most relevant and challenging LWC interview questions, equipping you with the knowledge and confidence to excel in your next interview.

1. Expand LWC. What do you mean by Salesforce Lightning?

LWC stands for Lightning Web Components. Salesforce Lightning is a component-based framework for Salesforce App development, designed to simplify the process for those without extensive programming experience. Its primary objective is to provide a user-friendly interface for creating dynamic web applications tailored for both mobile and desktop users.

2. How is LWC different from Aura?

The fundamental difference between LWC and Aura lies in the underlying technologies used for development. LWC-based lightning components are built using web stack tools, such as HTML and JavaScript, while Aura-based lightning components are built using HTML5 and JavaScript tools. This distinction makes LWC a more lightweight and efficient framework, resulting in faster performance compared to Aura components.

3. Can Aura Web Components and Lightning Web Components coexist together?

Yes, both Aura Lightning components and Lightning Web Components can coexist within the same application. This compatibility allows for a gradual transition from Aura to LWC, enabling developers to leverage the advantages of LWC while maintaining existing Aura components.

4. Describe the file structure of Lightning Web Components.

The file structure of Lightning Web Components typically consists of the following files:

• myComponent.html: The HTML template for the component.
• myComponent.js: The JavaScript file containing the component’s logic and functionality.
• myComponent.js-meta.xml: The metadata file for the component.
• myComponent.css: The CSS file for styling the component.
• myComponent.svg (optional): An SVG file for icons or graphics used within the component.

5. What are the rules for naming files in LWC?

When naming files in LWC, several rules must be followed:

• The file name must begin with a lowercase letter.
• The name can only contain alphanumeric or underscore characters.
• The name must be unique within the namespace.
• Whitespaces, hyphens, and consecutive underscores are not allowed.
• The name should not end with an underscore.

6. How do you iterate through a list in LWC?

In LWC, there are two primary ways to iterate through a list:

1. Using the for:each directive: This directive is used to render a set of elements based on an array or an object.

<template>    <ul>        <template for_each={items} for_item="item">            <li key={item.id}>{item.name}</li>        </template>    </ul></template>

1. Using an iterator: This approach involves manually iterating over an array or object using JavaScript constructs like for loops or array methods like map() or forEach().

get renderedItems() {    return this.items.map(item => {        return `<li key="${item.id}">${item.name}</li>`;    });}

7. What is the use of the @wire decorator in LWC?

The @wire decorator is used to specify a wire adapter, which provisions data to the component. When the wired service provides data, the component is rendered with that data. It is a powerful feature that allows seamless integration of components with various data sources, including Apex methods and Lightning Data Service (LDS).

8. Can you call a @wire function inside a JavaScript function?

No, you cannot call a @wire function inside a JavaScript function in LWC. The @wire decorator must be attached directly to a class property or method within the component class. Attempting to call a @wire function inside another function will result in a compilation error.

9. When is the @wire method/property called in the lifecycle of a component?

The @wire method or property is called immediately after the component is created (after the constructor) and whenever the reactive properties passed as parameters change.

10. What are lifecycle hooks in LWC? List and explain them.

Lifecycle hooks are callback methods triggered at specific phases of a component instance’s lifecycle. The lifecycle hooks supported in LWC are:

• Constructor: Called when the component is created.
• connectedCallback: Called when the element is inserted into a document. This hook flows from parent to child.
• renderedCallback: Called after every render of the component. This hook flows from child to parent.
• disconnectedCallback: Called when the element is removed from a document. This hook flows from parent to child.
• errorCallback: Called when a descendant component throws an error.

11. Is the @wire method called multiple times during the lifecycle of a component?

Yes, the @wire method can be called multiple times during the lifecycle of a component. It is called initially after the component is created and again whenever the reactive properties passed as parameters change.

12. What is the difference between event.stopPropagation() and event.preventDefault()?

• event.stopPropagation() prevents further propagation of the current event in the capturing and bubbling phases, essentially stopping the event from bubbling up the DOM tree.
• event.preventDefault() prevents the default action the browser would take for that event, such as following a link or submitting a form.

13. Are quick actions supported for LWC components?

Yes, quick actions are supported for LWC components in Salesforce orgs with Summer ’21 or later releases. However, it’s important to note that LWC quick actions are currently only supported on record pages.

14. What is a promise in async transactions? What are its different stages?

In asynchronous transactions, a promise is an object returned that notifies you about the completion or failure of the transaction. The different stages of a promise are:

• Pending: Waiting for the result.
• Fulfilled: The promise resulted in success.
• Rejected: The promise resulted in failure.

15. What is the difference between Promise and Promise.all?

A regular Promise represents a single asynchronous operation, whereas Promise.all takes an array of promises as input and returns a single promise that resolves when all promises in the array have resolved or rejects if any promise in the array rejects.

16. What are web components? Is LWC based on web components?

Web components are a set of standards that allow developers to create and reuse custom HTML elements with encapsulated functionality. They are based on four main pillars: HTML Templates, Custom Elements, Shadow DOM, and HTML Imports.

Yes, LWC is based on web components and follows the web component standards. Salesforce has added additional features like security, Lightning Data Service (LDS), and base components on top of the web component foundation.

17. Why do we extend LightningElement in LWC?

In LWC, we extend the LightningElement class because it is a custom wrapper on top of the HTMLElement class. LightningElement contains all the lifecycle hooks and other Salesforce-specific enhancements, making it easier to develop and integrate components within the Salesforce ecosystem.

18. How do you retrieve elements based on their ID in LWC?

In LWC, it’s recommended to use the data-id attribute instead of the standard id attribute to reference elements. This is because the id you define in LWC may be transformed into something different during rendering, making it unreliable for referencing elements. You can use this.template.querySelector('[data-id="myId"]') to retrieve an element based on its data-id.

19. How do you send data from a parent component to a child component in LWC?

To send data from a parent component to a child component in LWC, you need to expose a property or function in the child component using the @api decorator. Then, in the parent component, you can use querySelector to access the child component and set the value of the exposed property or call the exposed function.

20. How can you communicate between two child components that are not part of the same hierarchy?

In LWC, you can communicate between two child components that are not part of the same hierarchy by firing an event from one child component to the parent component, and then calling an exposed property or function of the other child component from the parent component.

21. What does composed: true mean in an event?

When composed: true is set for an event, it means that the event can bubble up inside the DOM and can also cross the Shadow DOM boundary. This allows the event to propagate beyond the component that dispatched it and be captured by elements outside the component’s Shadow DOM.

22. What are callback functions in LWC? Are they synchronous or asynchronous?

Callback functions in LWC are functions passed as parameters to other functions. They are neither inherently synchronous nor asynchronous; their execution depends on the context in which they are called. If a callback function is passed to a synchronous function, it will execute synchronously, and if it’s passed to an asynchronous function, it will execute asynchronously.

23. What is callback hell, and how can it be avoided?

Callback hell, also known as the “Pyramid of Doom,” occurs when multiple nested callbacks are used, leading to deeply indented and difficult-to-read code. This situation often arises when dealing with asynchronous operations that depend on the completion of previous operations.

To avoid callback hell, modern JavaScript provides alternative solutions like Promises and async/await, which make asynchronous code more readable and easier to maintain.

24. What are decorators in LWC? Explain the three decorators used in LWC.

Decorators in LWC are special syntax elements that add functionality to properties or functions. The three decorators used in LWC are:

• @track: Used to make properties reactive, ensuring that changes to the property trigger a re-render of the component.
• @wire: Used to specify a wire adapter, which provisions data to the component.
• @api: Used to expose properties or methods to other components, allowing for communication between components.

25. Can you use multiple decorators on a single property in LWC?

No, you cannot use multiple decorators on a single property in LWC. Each property can have only one decorator applied to it.

By mastering these LWC interview questions, you’ll be well-equipped to showcase your expertise and demonstrate your readiness for the role. Remember, practice is key to success, so make sure to familiarize yourself with hands-on examples and real-world scenarios to solidify your understanding further.

Good luck with your LWC interviews!