21 Essential React.js Interview Questions *

21 Essential React.js Interview Questions

Explain the Virtual DOM, and a pragmatic overview of how React renders it to the DOM.


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Explain the standard JavaScript toolchain, transpilation (via Babel or other compilers), JSX, and these items’ significance in recent development. What sort of tools might you use in the build steps to optimize the compiled output React code?

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[Legacy projects only: React < 16] Compare and contrast the various React Component lifecycle methods. How might understanding these help build certain interfaces/features?



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How would you create Higher Order Components (HOCs) in React?


[Legacy projects only: React < 15.5] Compare and contrast incorporating mixins and enforcing modularity in React Components. (extend, createClass and mixins, HOCs) Why would you use these techniques, and what are the drawbacks of each?


What is the significance of keys in React?


What is the significance of refs in React?


[Legacy projects only, < circa 2016] In a general overview, how might React Router and its techniques differ from more traditional JavaScript routers like Backbone’s Router?


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[Legacy projects only: React < 16.8] What are pure functional Components?


How might React handle or restrict Props to certain types, or require certain Props to exist?


At a high level, what is the virtual DOM (VDOM) and how does React use it to render to the DOM?


What is prop drilling and how can you avoid it?


Why do class methods need to be bound to a class instance, and how can you avoid the need for binding?


What is the StrictMode component and why would you use it?


What is the key architectural difference between a JavaScript library such as React and a JavaScript framework such as Angular? How would that impact the decision for a project to use one versus the other?

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Explain the positives and negatives of shallow rendering components in tests.


If you wanted a component to perform an action only once when the component initially rendered—e.g., make a web analytics call—how would you achieve this with a class component? And how would you achieve it with a function component?


What are the most common approaches for styling a React application?


How can automated tooling be used to improve the accessibility of a React application?


If you were working on a React application that was rendering a page very slowly, how would you go about investigating and fixing the issue?

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