Lightning Web Components (LWC) is Salesforce’s modern UI framework built using web standards like HTML, JavaScript, and modern ECMAScript. LWC offers a faster, more efficient way to build dynamic and responsive web apps in the Salesforce ecosystem.
As demand for skilled LWC developers continues to rise, understanding core LWC concepts is crucial for acing interviews in 2024. Below is a compilation of LWC Interview Questions and Answers for 2024 to help you prepare.
Table of Contents
1. What is LWC (Lightning Web Components)?
Answer:
LWC is a modern JavaScript framework built on native web standards for building components in Salesforce. It leverages features like custom elements, shadow DOM, and ECMAScript modules to create fast, efficient, and reusable UI components.
2. How is LWC different from Aura Components?
Answer:
- LWC is built on modern web standards, reducing the need for a proprietary framework, while Aura is Salesforce’s older component framework.
- LWC uses native browser APIs like Web Components, providing better performance and faster rendering.
- LWC offers a lighter and more optimized bundle size compared to Aura, which has more abstraction layers.
3. What are the key building blocks of LWC?
Answer:
- HTML: Used to define the template structure.
- JavaScript: Used for the business logic and controller functionality.
- CSS: To apply component-specific styling.
- Salesforce-specific modules: To handle Salesforce data (e.g., @wire, import).
- Metadata files: XML configuration that defines how the component can be used.
4. Explain the role of the @track decorator in LWC.
Answer:
@track was used to make a private property reactive in older versions of LWC (before version 1.0.0). However, in current LWC, all properties of objects are reactive by default, and @track is no longer needed. Now, you can use reactive properties without the decorator unless working with non-primitive types like objects or arrays.
5. What is the purpose of the @api decorator in LWC?
Answer:
The @api decorator is used to expose a property or method to other components. It makes the property accessible to the parent or other components that use the child component.
6. How do you share data between components in LWC?
Answer:
There are multiple ways to share data between components:
- Parent-to-child: Use the @api decorator to pass data via attributes.
- Child-to-parent: Use custom events to notify the parent component of changes.
- Sibling components: Use a pub-sub model for components that are not in a direct parent-child relationship.
7. What is a wire service in LWC, and how does it work?
Answer:
The wire service is a reactive service that delivers data from Salesforce to an LWC component. It automatically updates the component when the data changes. You use the @wire decorator to bind Salesforce data (Apex methods, records, or SOQL) to the component.
8. How do you call an Apex method from LWC?
Answer:
To call an Apex method from LWC, follow these steps:
- Use the @AuraEnabled decorator in the Apex class to make the method accessible.
- Import the Apex method into your LWC component using import.
- Call the method using the promise syntax.
import apexMethod from '@salesforce/apex/Controller.methodName';
apexMethod({ paramName: value })
.then(result => {
// handle result
})
.catch(error => {
// handle error
});
9. What is the Lightning Data Service (LDS) in LWC?
Answer:
LDS is used to interact with Salesforce data without writing Apex code. It offers methods to query, create, update, and delete records using the lightning-record-form, lightning-record-view-form, or @wire with LDS adapters like getRecord, getFieldValue, etc.
10. What is a shadow DOM in LWC?
Answer:
Shadow DOM is a browser technology used to encapsulate the internal structure of a component. It ensures that the styles and structure of a component do not leak outside its boundary and are not affected by external styles.
11. Can you explain the lifecycle hooks in LWC?
Answer:
LWC components have the following lifecycle hooks:
- constructor(): Called when the component is initialized.
- connectedCallback(): Invoked when the component is inserted into the DOM.
- renderedCallback(): Called after the component has rendered.
- disconnectedCallback(): Invoked when the component is removed from the DOM.
- errorCallback(): Captures any errors in the component or its children.
12. How can you create a reusable component in LWC?
Answer:
To create a reusable component:
- Build the component's logic in the JavaScript file.
- Define a flexible template in the HTML file, using slots if needed.
- Expose any necessary properties or methods using the @api decorator.
-
Reuse the component by including it in other components using
.
13. How do you handle events in LWC?
Answer:
In LWC, events are handled using the standard DOM event system. To dispatch an event, use the CustomEvent constructor in the child component. The parent component can handle the event using event listeners.
// Dispatching an event
this.dispatchEvent(new CustomEvent('myevent', { detail: { key: 'value' } }));
// Handling the event in the parent
<template>
<c-child-component onmyevent={handleEvent}></c-child-component>
</template>
handleEvent(event) {
console.log(event.detail.key);
}
14. What is a slot in LWC?
Answer:
Slots allow a parent component to pass HTML content into a child component. This makes components more flexible and reusable. Use the <slot> tag in the child component’s template to define where the parent’s content should be placed.
15. Explain the difference between lightning-record-form, lightning-record-view-form, and lightning-record-edit-form.
Answer:
- lightning-record-form: A simple form to view, create, or update a Salesforce record.
- lightning-record-view-form: Displays read-only data for a record.
- lightning-record-edit-form: Provides full control over how the form behaves and how the fields are laid out for editing records.
