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Advanced React Interview Questions and Answers

February 4, 2024


What are the advanced React interview questions and answers?

React, also known as React.js or ReactJS, is a front-end, open-source JavaScript library for building user interfaces using UI components.

React has been doing well for five years now, and there is no end in sight. As you probably already know, it’s getting more advanced every day, so you need to be well-prepared for your next interview.

We’ve put together some of the most frequently asked advanced React questions in this post.

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10+ Advanced React Interview Questions and Answers

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

A Higher-Order Component (HOC) is an advanced technique in React to reuse component logic. However, you should also know that HOC is not exactly part of the React API. They are a pattern that emerges from the compositional nature of React.

Check out the React documentation for more.

2. What are synthetic events in React?

React implements a synthetic event system that brings consistency and high performance to React applications and interfaces.

A synthetic event is a cross-browser wrapper around the browser’s native event. It has the same interface as the browser’s native event, including stopPropagation() and PreventionDefault(), except that events work the same in all browsers.

3. What is Redux Thunk used for?

Redux is a popular library for front-end development. Applications built using Redux are easy to test and can run seamlessly in multiple framework environments.

Redux Thunk is a popular middleware for React Redux. You can create services that return a function, hence the name Thunk.

Here is an excerpt from GitHub:

“The Redux Thunk middleware lets you write action creators that return a function instead of an action.”

It can delay the dispatch of action if a specific condition is met. This allows you to handle sending actions asynchronously.

The most common use case for Redux Thunk is to communicate asynchronously with an external API to retrieve or save data. Redux Thunk makes it easy to send actions that follow a request’s lifecycle to an external API.

4. What are some of the features of the ReactJS framework?

  • React allows Data Binding where developers can choose which elements users can access and which elements are hidden. Thanks to this feature, the applications’ security is also flawless.
  • React has a one-way data flow.
  • React uses Virtual DOM instead of RealDOM. (React DOM structure will be explained in detail in the next question.)
  • React mainly uses client-side rendering.

5. How do updates work in React?

  • On the first load, ReactDOM.render() will create the Virtual DOM tree and real DOM tree.
  • As React works on Observable patterns, when an event(like key press, left click, api response, etc.) occurs, Virtual DOM tree nodes are notified for props change. If the properties used in that node are updated, the node is updated; else is left as it is.
  • React compares Virtual DOM with real DOM and updates real DOM. This process is called Reconciliation. React uses Diffing algorithm techniques of Reconciliation.
  • Updated real DOM is repainted on the browser.

6. What are the advantages of using Flux?

Developers can build applications without being disturbed by the complex interactions between data sources. Flux has a better-structured data flow – one-way. Being unidirectional is the key feature of Flux.

Flux offers many benefits, the most important of which are:

It ensures uniformity of code execution, thus avoiding Runtime errors.
It increases the efficiency of the application by helping to make updates more effectively with the one-way data flow.

7. What are webpack and browserify?

Webpack and Browserify do the same job, rendering your code for use in a specific place. The result of such processing is one or more clusters.

However, Webpack and Browserify differ in many ways.
Webpack provides many tools by default, whereas Browserify can only do this after downloading the add-ons, but using both results in the same outcomes.

Webpack is a popular module packaging system built on Node.js. It can handle not only the merging and minification of JavaScript and CSS files, but also other assets such as image files (spriting) through the use of plugins.

Browserify helps solve this by allowing you to use CommonJS style require(‘filename’) in the code.

8. How to re-render a React component?

React automatically Re-Renders the components whenever any of its props or state is updated.

Class Components provide you with a built-in method to trigger a Re-Render. Simply use forceUpdate method to force React to Re-Render the component.

Functional Components don’t have a forceUpdate method for ease of use. You can use the useState hook to simulate an update or create a custom hook too.

9. What are the different phases of React JS component lifecycle ?

Lifecycle methods: Developing each component in ReactJS involves using different lifecycle methods. All the lifecycle methods used to create such components together make up the component’s lifecycle. They are defined as a set of functions called at various stages of a component. Each stage of lifecycle components contains some specific lifecycle methods related to that stage.

There are four different phases of the React component’s lifecycle:

Initialization: The React component prepares to set the initial state and default hardware at this stage.

Mounting: The React component is ready to be mounted in the browser DOM. This phase covers the componentWillMount and componentDidMount lifecycle methods.

Updating: At this stage, the component is updated in two ways, new accessories are sent, and its status is updated. This phase covers the mustComponentUpdate, componentWillUpdate, and componentDidUpdate lifecycle methods.

Unmounting: The component is not required in this final step and is stripped from the browser DOM. This phase contains the componentWillUnmount lifecycle method.

10. What is prop drilling and how can you avoid it?

When building a React app, a deeply nested component is often needed to use data provided by another component much higher in the hierarchy. It’s to pass a prop from each component in the hierarchy to the next, from the source component to the deeply nested component. This is called prop drilling.

A common approach to avoid prop drilling is to use React context. This allows a Provider component that provides the data to be defined and enables nested components to consume context data via a Consumer component or a useContext hook.

11. What is StrictMode in React?

StrictMode is a tool for highlighting potential problems in an application. Like Fragment, StrictMode doesn’t create a visible UI. It enables additional checks and alerts for descendants.

Strict mode controls are run only in development mode; they don’t affect the production structure.

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