70+ LWC Interview Questions: Master the Must-Know Concepts in 2024

LWC is a programming model developed by Salesforce. Its main purpose is to help developers create reusable and efficient user interfaces that are compatible with the Lightning Experience and Salesforce mobile app​​.

LWC-based lightning components are built using web stack tools, whereas Aura-based lightning components are built using HTML5 and JavaScript tools.

To use third-party JavaScript libraries in LWC, you must upload the library as a static resource, then import it into your component using an ‘import’ statement with the resource URL. Load the script using the loadScript() function from the platformResourceLoader module within the renderedCallback() lifecycle hook​.

The @wire decorator in LWC is used to provision data, metadata, and other information from Salesforce to LWC components. It’s reactive, meaning it automatically re-renders components when input changes.

Aura components can communicate with Lightning Web Components using Public APIs and Events. LWC can be embedded within Aura Components, but the reverse is not possible​​.

Tools in Salesforce Lightning include Lightning Component Framework, Lightning Connect, Lightning App Builder, Lightning Schema Builder, and Lightning Process Builder​​.

Testing LWC involves using Jest, a JavaScript testing framework. Tests are written in .test.js files inside the __tests__ folder of your component directory. Each test file should import the component to be tested and use describe() function for grouping related tests, with it() function for individual tests and expect() function for assertions.

The @api decorator in LWC is used to make a property or method publicly accessible. This allows parent components to set or access the decorated properties and methods in a child component, enabling communication between components​.

n LWC, error handling is done using try-catch-finally blocks in JavaScript. The ‘try’ block contains the code that may potentially throw an exception, with the ‘catch’ block handling it and the ‘finally’ block executing regardless of the outcome. Additionally, LWC provides ‘@wire’ decorator for calling Apex methods, and any error during this operation is captured in the ‘error’ property of the wire service.

In LWC, dependent picklists can be handled by using the getPicklistValues wire adapter from the lightning/uiObjectInfoApi module. This wire adapter fetches the picklist values based on record type id and field API name, allowing developers to dynamically generate picklist options based on dependencies​.

In LWC, events are used for communication between components. Custom events are created and dispatched from a component, and other components can listen and respond to these events. Standard DOM events can also be used for user interactions like clicks and input changes.

The @api decorator marks a field as public, allowing it to be set by a parent component. The @track decorator, used for reactivity in LWC, is no longer required for primitive data types as changes are tracked automatically, but is still needed for objects and arrays.

The shadow DOM provides encapsulation for LWC components. It isolates the component’s markup and style, preventing styles from leaking in or out and markup from being accidentally manipulated by other components. This encapsulation is automatic in LWC.

A decorator in LWC is a special syntax used to modify class properties and methods. Common decorators include @api, @track, and @wire. They are used to define public properties, reactive properties, and to wire data to a component, respectively.

LWC offers modern web standards compatibility, better performance, Aura components interoperability, support for modern JavaScript features, and enhanced testing and debugging capabilities.

LWC components can be nested inside Aura components, but Aura components cannot be used within LWC. This allows for gradual migration from Aura to LWC.

Events in LWC are used for inter-component communication. Custom events are created and dispatched by a component for other components to listen and respond to. Standard DOM events are also used for user interaction.

Core modules in LWC are JavaScript modules that provide basic functionalities and are imported from the ‘lwc’ namespace. Key modules include LightningElement, @api, @track, and @wire. These modules help in defining the component’s behavior, exposing public properties and methods, tracking changes, and wiring data.

Communication between parent and child components in LWC can be achieved using the @api decorator to expose properties and methods, allowing the parent component to set or access them. Additionally, the child component can emit custom events, which the parent component listens for and handles​.

Data sharing in LWC is managed through a reactive wire service and properties. The wire service provisions data from Salesforce, automatically re-rendering components when inputs change. Properties are used for parent-to-child communication, updating the child’s property when the parent’s property value changes​.

Errors and exceptions in LWC are typically handled using try-catch-finally blocks. The try block contains code that might throw an exception, the catch block handles the error, and the finally block executes code regardless of whether an exception occurred. Additionally, errors in wire services are captured in the error property.

Best practices in LWC include using dispatcher components to listen and relay events, segregating business-level events from low-level events, clearing cache data when possible, and utilizing helper methods for repeated logic​​.

The key difference between Aura and LWC is that LWC-based lightning components are built using web stack tools and follow modern web standards, while Aura-based lightning components are built using HTML5 and JavaScript tools. LWC generally offers better performance and more modern features.

The LWC architecture mainly consists of three components: the LWC Framework, Base Lightning Components, and Salesforce Bindings. These components work together to provide a comprehensive development environment for building Salesforce apps​​.

The purpose of LWC is to provide a modern framework for building efficient and reusable user interfaces on the Salesforce platform. It leverages standard web technologies to deliver high-performance UI components that are compatible with the Salesforce ecosystem​​.

CSS in LWC is scoped to the component and is defined in a separate .css file within the component bundle. The styles declared in this file apply only to the component’s template and don’t leak to other components.

Yes, LWC can work with external APIs. You can call external APIs from Apex methods and expose these methods to LWC using @AuraEnabled annotation. Then, use the @wire or imperative approach to call these Apex methods from your LWC.

LWC provides several lifecycle hooks, such as constructor(), connectedCallback(), renderedCallback(), disconnectedCallback(), and errorCallback(). Each of these hooks is called at different stages in the lifecycle of the component.

In LWC, events follow the standard DOM event propagation model, which includes three phases: capturing, target, and bubbling. By default, events bubble up from the child to the parent, but this behavior can be modified.

Slots in LWC are a way to create a placeholder inside a component that can be filled with custom content. They are used for content projection, allowing child components to be placed within the layout of a parent component.

An Apex method can be called from an LWC either using the @wire decorator for a reactive approach or using an imperative call. Apex methods should be exposed to LWC using the @AuraEnabled annotation.

The track property in LWC was initially used to monitor changes in objects and arrays for reactivity. However, since the Spring ’20 release, LWC automatically tracks changes in fields, so the use of @track is reduced.

Data security in LWC is ensured by adhering to Salesforce’s security best practices, such as enforcing CRUD and FLS (Field Level Security), using secure Apex methods, and avoiding the exposure of sensitive data in JavaScript.

Yes, LWC components are fully supported in the Salesforce Mobile App. They are designed to be mobile-responsive, making them suitable for use in both desktop and mobile interfaces.

Locker Service in LWC is a security architecture that isolates components in their namespace, preventing them from accessing each other’s state. It enhances security by enforcing best practices in JavaScript and DOM manipulation.

LWC can be deployed using Salesforce CLI, Change Sets, Unmanaged Packages, or Metadata API. Each method serves different deployment needs, from individual component deployment to full-scale application releases.

Enhancing LWC performance involves optimizing component code, minimizing the use of JavaScript for DOM manipulation, using lazy loading for components, optimizing Apex calls, and leveraging browser caching.

The LightningElement base class is the core of LWC. It provides the basic functionalities needed for creating custom elements and includes lifecycle hooks, reactive properties, and rendering capabilities.

Internationalization in LWC can be implemented using custom labels, lightning-formatted-text, and lightning-formatted-number components, which automatically handle locale-specific formats.

Reactive properties in LWC are properties that trigger the component to re-render when their values change. This reactivity is automatically handled by LWC for primitive data types and can be enforced for objects and arrays using @track.

Yes, LWC can interact with Salesforce data without Apex using wire adapters like getRecord, getListUi, and getObjectInfo from the lightning/uiRecordApi module, which allow read access to Salesforce data.

Navigation in LWC is handled using the lightning/navigation service. This service provides methods for navigating to Salesforce pages, records, and objects within the Lightning Experience and Salesforce mobile app.

Component markup in LWC is more aligned with modern web standards, using standard HTML and JavaScript, whereas Aura has its custom syntax and framework-specific tags.

State management in LWC can be done through reactive properties, JavaScript variables, and shared services. Complex state management might involve using patterns like Redux.

Testing LWC involves writing unit tests using Jest. Best practices include testing both positive and negative scenarios, mocking wire service calls and Apex methods, and ensuring code coverage.

The @wire decorator is used to read data from Salesforce, often from an Apex method or a standard Salesforce API. When the data changes, the wire service provisions the new data, and the component re-renders automatically.

Common tools in Salesforce Lightning include the Lightning Component Framework, Lightning Connect, Lightning App Builder, Lightning Schema Builder, and Lightning Process Builder. These tools collectively support the development and integration of custom functionalities in Salesforce.

Salesforce Developer Experience (SFDX) refers to a set of tools and features provided by Salesforce to enhance the development experience on its platform. SFDX includes functionalities like source-driven development, scratch orgs, and continuous integration/continuous delivery.

The @wire method is automatically invoked in a Lightning Web Component when the component is connected to the DOM or when any reactive property that the method depends on changes. You may like Salesforce Apex Trigger Examples (Advanced).

Contrary to common belief, the data returned by imperative Apex methods in LWC is mutable. Developers have the ability to change the data once it’s received in the component.

LWC components are faster than Aura components primarily because they are built using modern web standards and a lightweight framework. The absence of an abstraction layer in LWC leads to better performance.

Lightning Web Components can communicate with Aura components using public APIs and events. This interoperability allows for a combination of both LWC and Aura components in a Salesforce application.

Although LWC is powerful, it has some limitations like lack of support for the Lightning Experience Console, absence of two-way binding, and restrictions in using Email templates.

Slots in LWC allow for the creation of reusable components by enabling component composition. A slot acts as a placeholder within a component where other components can be inserted, facilitating the creation of complex and nested structures.

Testing LWC components typically involves using Jest, a JavaScript testing framework. Developers write unit tests in .test.js files, utilizing functions like describe() for grouping tests and it() for individual test cases

LWC adheres to Salesforce’s security model, ensuring compliance with CRUD and FLS (Field Level Security). This involves respecting user permissions an

Lightning Message Service (LMS) facilitates communication across the Salesforce UI, including LWC, Aura components, and Visualforce pages. It is useful for passing messages between components that are not in a direct hierarchy.

Decorators like @api, @track, and @wire in LWC are special JavaScript annotations that add metadata and functionality to class properties and methods. They are used to define public properties, track property changes, and connect components to Salesforce data.

To optimize performance with large lists, use techniques like pagination, lazy loading, and virtual scrolling. These approaches help in rendering only a subset of items at a time, reducing the load on the browser.

The render() method in LWC is a lifecycle hook used to override the default rendering process. It can be used to conditionally render different templates based on component state.

Reactive wire adapters in LWC are used to automatically provision data from Salesforce when input parameters change, triggering a re-render of the component.

Dynamic styling in LWC can be achieved using JavaScript to manipulate CSS classes and styles. The classList API is commonly used for adding or removing CSS classes dynamically.

Salesforce schema references in LWC, like field and object names, can be imported from the @salesforce/schema module. This approach ensures referential integrity and avoids hard-coding API names.

LWC components can be debugged using browser developer tools. Console logs, breakpoints, and the Performance tab are typical tools used. Salesforce-specific debugging can be done using the Salesforce Developer Console’s debug logs.

Event handling in LWC follows standard web component models, primarily using CustomEvent for component communication. In contrast, Aura uses its event system, which is more framework-specific.

Inheritance in LWC can be achieved by extending classes. A common pattern is to have a base LWC component class that defines shared behavior, and then other components extend this class to inherit its properties and methods.

LWC components, while primarily designed for the Salesforce platform, can be used outside Salesforce in standalone web applications. This is possible because LWC is based on standard web technologies.

The slot tag in LWC is used for content projection, allowing child components to be placed within the layout of a parent component. It provides a way to create flexible and reusable component templates.

Mobile responsiveness in LWC can be handled using CSS media queries and the Salesforce Lightning Design System (SLDS), which provides a responsive grid system and utility classes to build responsive layouts.