ReactJS Interview Questions on Components

1. What are the components in React?

Components are the building blocks of any React application, and a single app usually consists of multiple components. A component is essentially a piece of the user interface. It splits the user interface into independent, reusable parts that can be processed separately.

There are two types of components in React:

• Functional Components: These components have no state and only contain render methods. Therefore, they are also called stateless components. They may derive data from other components as props (properties).
• Class Components: These components can hold and manage their state and have a separate render method to return JSX on the screen. They are also called Stateful components, as they can have a state.

2. What is the use of render() in React?

render() is a lifecycle method in class components that returns the JSX to be displayed on the screen. It’s called every time the component’s state or props change, updating the UI accordingly.

3. What is a state in React?

• The state is a built-in React object that contains data or information about the component. A component’s state can change over time, and whenever it changes, the component re-renders.
• The state change can occur as a response to user action or system-generated events. It determines the component’s behavior and rendering method.

4. What are props in React?

Props (short for properties) are inputs passed from parent to child components, allowing data and configuration to flow into the component. Props are read-only and cannot be modified within the child component.

5. How do you pass props between components?

Props are passed from a parent to a child component by including them as attributes in the child component’s JSX tag. The child component then accesses the props through props.propertyName.

6, What are the differences between state and props?

State is a local, mutable data structure managed within a component, whereas props are immutable data passed from a parent to a child component. State is used for dynamic data within the component, while props control component behavior from outside.

7. What is a higher-order component in React?

A higher-order component (HOC) is a function that takes a component and returns an enhanced component, adding functionality or modifying behavior. HOCs are used for cross-cutting concerns like authentication, logging, or data fetching.

8. How can you embed two or more components into one?

You can embed components by nesting them within a parent component or using composition to render multiple components together. You can also pass components as children or props for dynamic embedding