1. What is React Fiber?

Answer:

React Fiber is the reconciliation engine in React — it’s the core algorithm behind how React updates the DOM.

Introduced in React 16, Fiber replaced React's older reconciliation algorithm and made React faster, interruptible, and smarter in handling UI updates.

⚙️ How React Fiber Works:

  1. Begin phase: React walks the tree from top → down and builds the Fiber tree.
  2. Complete phase: React walks from bottom → up and prepares DOM mutations.
  3. Commit phase: Applies changes to the real DOM in a single step.

Each phase can be paused, resumed, or aborted — making React more responsive.

2. How to perform automatic redirect after login?

Answer:

The react-router package will provide the component <Redirect> in React Router. Rendering of a <Redirect> component will navigate to a newer location. In the history stack, the current location will be overridden by the new location just like the server-side redirects.

import React, { Component } from 'react'
import { Redirect } from 'react-router'
export default class LoginDemoComponent extends Component {
 render() {
   if (this.state.isLoggedIn === true) {
     return <Redirect to="/your/redirect/page" />
   } else {
     return <div>{'Please complete login'}</div>
   }
 }
}

3. Differentiate React Hooks vs Classes?

Answer:

React Hooks Classes
It is used in functional components of React. It is used in class-based components of React.
It will not require a declaration of any kind of constructor. It is necessary to declare the constructor inside the class component.
It does not require the use of this keyword in state declaration or modification. Keyword this will be used in state declaration (this.state) and in modification (this.setState()).
It is easier to use because of the useState functionality. No specific function is available for helping us to access the state and its corresponding setState variable.
React Hooks can be helpful in implementing Redux and context API. Because of the long setup of state declarations, class states are generally not preferred.