Top 10 LWC Interview Questions

1. What is Lightning Web Components (LWC) and how does it differ from Aura Components?

Lightning Web Components (LWC) is a modern framework for building web components on the Salesforce platform. It leverages web standards and can coexist with Aura components. LWC is faster and more efficient due to its lightweight nature and adherence to modern web standards. Unlike Aura, LWC promotes the use of standard JavaScript and HTML, making it easier for developers familiar with web development to adopt.

2. Explain the component lifecycle in LWC.

LWC components have a lifecycle managed by the framework, with hooks that allow you to perform actions at key points: constructor(): Invoked when the component is created. connectedCallback(): Called when the component is inserted into the DOM. render(): Determines the component's template. renderedCallback(): Invoked after the component and its children are rendered. disconnectedCallback(): Called when the component is removed from the DOM.

3. How does data binding work in LWC?

LWC uses a reactive data binding system. Properties decorated with @track or @api are reactive. When their values change, the view updates automatically to reflect the changes. JavaScript properties are reactive by default for primitive values, but @track is needed for tracking changes in object or array properties.

4. What are decorators in LWC, and can you name a few?

Decorators are JavaScript functions that add metadata and extra functionality to class properties or methods. In LWC, common decorators include: @api: Marks a public property or method that can be accessed by other components. @track: Used to monitor changes to objects and arrays, making the template reactive to data changes. @wire: Allows you to wire a property or function to a data source (like an Apex method or Salesforce data).

5. Describe how events are handled in LWC.

Events in LWC follow the DOM event model. Components can dispatch standard or custom events using this.dispatchEvent(new CustomEvent('eventname', options)). Event handlers can be added in the component's template using the on[eventname] syntax or programmatically using addEventListener.

6. What is the @wire service, and how is it used?

The @wire service allows components to read data from Salesforce orgs reactively. It can be used with Apex methods, Salesforce data services like getRecord, and custom wire adapters. The wired property or function updates automatically when the source data changes.

7. Explain the significance of the slot tag in LWC.

The slot tag enables content projection, allowing child components to be placed within designated areas of a parent component's template. This is useful for creating reusable and flexible component designs.

8. How do you communicate between LWC components?

Components can communicate using: Public properties and methods (@api): For parent-to-child communication. Events: For child-to-parent communication, or between sibling components via a common parent. Publish-subscribe model: For loosely coupled components, often used for communication across the component tree.

9. Can LWC and Aura components interoperate? How?

Yes, LWC and Aura components can interoperate. An LWC component can be used inside an Aura component by including it as if it were an Aura component. Conversely, to use an Aura component inside LWC, the Aura component must implement the lightning:isUrlAddressable interface, and it can then be embedded using lightning:container or via navigation using standard web techniques.

10. What are some security features inherent in LWC?

LWC enforces strict security features, including: Locker Service: Enforces encapsulation and provides secure wrappers around standard DOM APIs. Content Security Policy (CSP): Helps prevent XSS attacks by controlling the resources the browser is allowed to load. Secure Wrappers: Provide secure access to DOM elements, enforcing the principle of least privilege.