React Component

React components are the fundamental building blocks of a React application. They encapsulate parts of the user interface, making it easy to create complex UIs from smaller, isolated pieces of code. Components can be either functional or class-based, and they can manage their own state and lifecycle methods. Here’s an in-depth look at React components:

Types of Components

Functional Components
Class Components

Functional Components

Functional components are simpler and are typically used for components that don’t need to manage state or lifecycle methods. They are just JavaScript functions that accept props as an argument and return React elements.

Example of a functional component:


//src/MyComponent.js
import React from 'react';

function Welcome() {
  return Hello World!;
}
export default Welcome;

In this example, welcome is a functional component and returns a React element.

Class Components

Class components are more feature-rich. They allow you to use additional features like local state and lifecycle methods. Class components extend React.component.

Example of a class component:


src/Greetings.js
import React, { Component } from 'react';

class Greetings extends React.Component {
  render() {
    return Hello World!;
  }
}

export default Greetings;

In this example, Greetings is a class component that renders the same output as the functional component.

Rendering a component

Rendering a component in React.js involves creating a component and then rendering it in the DOM.

Import and use the component in your main application file (src/App.js).

Rendering a function component


// src/App.js
import React from 'react';
import MyComponent from './MyComponent';

const App = () => {
  return (
    <div>
       <MyComponent />
     </div>
  );
};

export default App;

In this example, output will be Hello World!

Rendering a class component

It will be same as a function component


// src/App.js
import React from 'react';
import Greetings from './Greetings';

const App = () => {
  return (
    <div>
      <Greetings />
    </div>
  );
};

export default App;

In this example, output will be Hello World!

React Component – Interview Questions

Q 1: What is a component in React?

Ans: A component is a reusable piece of UI that can contain logic, state, and rendering code.

Q 2: How many types of components are there in React?

Ans: Mainly two types: Function Components and Class Components.

Q 3: Why are components reusable?

Ans: Components encapsulate logic and UI, allowing reuse across multiple parts of an application.

Q 4: What is component-based architecture?

Ans: It divides the UI into independent, reusable components for better maintainability.

Q 5: What is a root component?

Ans: The main component (usually App.js) that acts as the entry point of the React app.