Amay Jain
Amay Jain (@BrajBliss)


Amay Jain (@BrajBliss)


ReactJS Interview Questions - Set 1

And this starts the ReactJS series.

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Amay Jain
·Nov 7, 2022·

4 min read

ReactJS Interview Questions - Set 1

Photo by Lautaro Andreani on Unsplash

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Table of contents

  • Hooks
  • Class Based Life Cycle Methods
  • Pure Components
  • Higher Order Components
  • Virtual DOM
  • Redux

For the JS Questions, you should check out:


Hooks are a new addition in React 16.8. They let you use state and other React features without writing a class. Hooks are backwards-compatible.
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Class Based Life Cycle Methods

We have seen so far that React web apps are actually a collection of independent components that run according to the interactions made with them. Every React Component has a lifecycle of its own, lifecycle of a component can be defined as the series of methods that are invoked in different stages of the component’s existence. The definition is pretty straightforward but what do we mean by different stages? A React Component can go through four stages of its life as follows.

  • Initialization: This is the stage where the component is constructed with the given Props and default state. This is done in the constructor of a Component Class.
  • Mounting: Mounting is the stage of rendering the JSX returned by the render method itself.
  • Updating: Updating is the stage when the state of a component is updated and the application is repainted.
  • Unmounting: As the name suggests Unmounting is the final step of the component lifecycle where the component is removed from the page.

React provides the developers a set of predefined functions that if present is invoked around specific events in the lifetime of the component. Developers are supposed to override the functions with desired logic to execute accordingly. We have illustrated the gist in the following diagram.

image.png Read More

Pure Components

React.PureComponent is similar to React.Component. The difference between them is that React.Component doesn’t implement shouldComponentUpdate(), but React.PureComponent implements it with a shallow prop and state comparison. If your React component’s render() function renders the same result given the same props and state, you can use React.PureComponent for a performance boost in some cases.
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Higher Order Components

A higher-order component (HOC) is an advanced technique in React for reusing component logic. HOCs are not part of the React API, per se. They are a pattern that emerges from React’s compositional nature.
Concretely, a higher-order component is a function that takes a component and returns a new component.
Reason to use Higher-Order component:

  • Easy to handle
  • Get rid of copying the same logic in every component
  • Makes code more readable

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Virtual DOM

The virtual DOM (VDOM) is a programming concept where an ideal, or “virtual”, representation of a UI is kept in memory and synced with the “real” DOM by a library such as ReactDOM. This process is called reconciliation. This approach enables the declarative API of React: You tell React what state you want the UI to be in, and it makes sure the DOM matches that state. This abstracts out the attribute manipulation, event handling, and manual DOM updating that you would otherwise have to use to build your app.
Since “virtual DOM” is more of a pattern than a specific technology, people sometimes say it to mean different things. In React world, the term “virtual DOM” is usually associated with React elements since they are the objects representing the user interface. React, however, also uses internal objects called “fibers” to hold additional information about the component tree. They may also be considered a part of “virtual DOM” implementation in React. Read More


React Redux is the official React UI bindings layer for Redux. It lets your React components read data from a Redux store, and dispatch actions to the store to update state. Redux is a state managing library used in JavaScript apps. It simply manages the state of your application or in other words, it is used to manage the data of the application.

It makes easier to manage state and data. As the complexity of our application increases. At the start, it is hard to understand but it really helps to build complex applications. In starting, it feels like a lot of work, but it is really helpful. Redux helps you write applications that behave consistently, run in different environments (client, server, and native), and are easy to test.

Centralizing your application's state and logic enables powerful capabilities like undo/redo, state persistence, and much more. The Redux DevTools make it easy to trace when, where, why, and how your application's state changed. Redux's architecture lets you log changes, use "time-travel debugging", and even send complete error reports to a server. Redux works with any UI layer, and has a large ecosystem of addons to fit your needs.
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That ends the first set of concepts. Make sure to follow me on Twitter🐦 for more updates! Check out the second part.

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