Reactjs Interview Questions

React Interview Questions & Answers

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Table of Contents

No. Questions
Core React
1 What is React?
2 What are the major features of React?
3 What is JSX?
4 What is the difference between Element and Component?
5 How to create components in React?
6 When to use a Class Component over a Function Component?
7 What are Pure Components?
8 What is state in React?
9 What are props in React?
10 What is the difference between state and props?
11 Why should we not update the state directly?
12 What is the purpose of callback function as an argument of setState()?
13 What is the difference between HTML and React event handling?
14 How to bind methods or event handlers in JSX callbacks?
15 How to pass a parameter to an event handler or callback?
16 What are synthetic events in React?
17 What are inline conditional expressions?
18 What is “key” prop and what is the benefit of using it in arrays of elements?
19 What is the use of refs?
20 How to create refs?
21 What are forward refs?
22 Which is preferred option with in callback refs and findDOMNode()?
23 Why are String Refs legacy?
24 What is Virtual DOM?
25 How Virtual DOM works?
26 What is the difference between Shadow DOM and Virtual DOM?
27 What is React Fiber?
28 What is the main goal of React Fiber?
29 What are controlled components?
30 What are uncontrolled components?
31 What is the difference between createElement and cloneElement?
32 What is Lifting State Up in React?
33 What are the different phases of component lifecycle?
34 What are the lifecycle methods of React?
35 What are Higher-Order components?
36 How to create props proxy for HOC component?
37 What is context?
38 What is children prop?
39 How to write comments in React?
40 What is the purpose of using super constructor with props argument?
41 What is reconciliation?
42 How to set state with a dynamic key name?
43 What would be the common mistake of function being called every time the component renders?
44 Is lazy function supports named exports?
45 Why React uses className over class attribute?
46 What are fragments?
47 Why fragments are better than container divs?
48 What are portals in React?
49 What are stateless components?
50 What are stateful components?
51 How to apply validation on props in React?
52 What are the advantages of React?
53 What are the limitations of React?
54 What are error boundaries in React v16
55 How error boundaries handled in React v15?
56 What are the recommended ways for static type checking?
57 What is the use of react-dom package?
58 What is the purpose of render method of react-dom?
59 What is ReactDOMServer?
60 How to use InnerHtml in React?
61 How to use styles in React?
62 How events are different in React?
63 What will happen if you use setState in constructor?
64 What is the impact of indexes as keys?
65 Is it good to use setState() in componentWillMount() method?
66 What will happen if you use props in initial state?
67 How do you conditionally render components?
68 Why we need to be careful when spreading props on DOM elements??
69 How you use decorators in React?
70 How do you memoize a component?
71 How you implement Server-Side Rendering or SSR?
72 How to enable production mode in React?
73 What is CRA and its benefits?
74 What is the lifecycle methods order in mounting?
75 What are the lifecycle methods going to be deprecated in React v16?
76 What is the purpose of getDerivedStateFromProps() lifecycle method?
77 What is the purpose of getSnapshotBeforeUpdate() lifecycle method?
78 Do Hooks replace render props and higher order components?
79 What is the recommended way for naming components?
80 What is the recommended ordering of methods in component class?
81 What is a switching component?
82 Why we need to pass a function to setState()?
83 What is strict mode in React?
84 What are React Mixins?
85 Why is isMounted() an anti-pattern and what is the proper solution?
86 What are the Pointer Events supported in React?
87 Why should component names start with capital letter?
88 Are custom DOM attributes supported in React v16?
89 What is the difference between constructor and getInitialState?
90 Can you force a component to re-render without calling setState?
91 What is the difference between super() and super(props) in React using ES6 classes?
92 How to loop inside JSX?
93 How do you access props in attribute quotes?
94 What is React PropType array with shape?
95 How to conditionally apply class attributes?
96 What is the difference between React and ReactDOM?
97 Why ReactDOM is separated from React?
98 How to use React label element?
99 How to combine multiple inline style objects?
100 How to re-render the view when the browser is resized?
101 What is the difference between setState and replaceState methods?
102 How to listen to state changes?
103 What is the recommended approach of removing an array element in react state?
104 Is it possible to use React without rendering HTML?
105 How to pretty print JSON with React?
106 Why you can’t update props in React?
107 How to focus an input element on page load?
108 What are the possible ways of updating objects in state?
110 How can we find the version of React at runtime in the browser?
111 What are the approaches to include polyfills in your create-react-app?
112 How to use https instead of http in create-react-app?
113 How to avoid using relative path imports in create-react-app?
114 How to add Google Analytics for react-router?
115 How to update a component every second?
116 How do you apply vendor prefixes to inline styles in React?
117 How to import and export components using react and ES6?
118 What are the exceptions on React component naming?
119 Why is a component constructor called only once?
120 How to define constants in React?
121 How to programmatically trigger click event in React?
122 Is it possible to use async/await in plain React?
123 What are the common folder structures for React?
124 What are the popular packages for animation?
125 What is the benefit of styles modules?
126 What are the popular React-specific linters?
127 How to make AJAX call and In which component lifecycle methods should I make an AJAX call?
128 What are render props?
React Router
129 What is React Router?
130 How React Router is different from history library?
131 What are the components of React Router v4?
132 What is the purpose of push and replace methods of history?
133 How do you programmatically navigate using React router v4?
134 How to get query parameters in React Router v4
135 Why you get “Router may have only one child element” warning?
136 How to pass params to history.push method in React Router v4?
137 How to implement default or NotFound page?
138 How to get history on React Router v4?
139 How to perform automatic redirect after login?
React Internationalization
140 What is React-Intl?
141 What are the main features of React Intl?
142 What are the two ways of formatting in React Intl?
143 How to use FormattedMessage as placeholder using React Intl?
144 How to access current locale with React Intl
145 How to format date using React Intl?
React Testing
146 What is Shallow Renderer in React testing?
147 What is TestRenderer package in React?
148 What is the purpose of ReactTestUtils package?
149 What is Jest?
150 What are the advantages of Jest over Jasmine?
151 Give a simple example of Jest test case
React Redux
152 What is Flux?
153 What is Redux?
154 What are the core principles of Redux?
155 What are the downsides of Redux compared to Flux?
156 What is the difference between mapStateToProps() and mapDispatchToProps()?
157 Can I dispatch an action in reducer?
158 How to access Redux store outside a component?
159 What are the drawbacks of MVW pattern
160 Are there any similarities between Redux and RxJS?
161 How to dispatch an action on load?
162 How to use connect from React Redux?
163 How to reset state in Redux?
164 Whats the purpose of at symbol in the redux connect decorator?
165 What is the difference between React context and React Redux?
166 Why are Redux state functions called reducers?
167 How to make AJAX request in Redux?
168 Should I keep all component’s state in Redux store?
169 What is the proper way to access Redux store?
170 What is the difference between component and container in React Redux?
171 What is the purpose of the constants in Redux?
172 What are the different ways to write mapDispatchToProps()?
173 What is the use of the ownProps parameter in mapStateToProps() and mapDispatchToProps()?
174 How to structure Redux top level directories?
175 What is redux-saga?
176 What is the mental model of redux-saga?
177 What are the differences between call and put in redux-saga
178 What is Redux Thunk?
179 What are the differences between redux-saga and redux-thunk
180 What is Redux DevTools?
181 What are the features of Redux DevTools?
182 What are Redux selectors and Why to use them?
183 What is Redux Form?
184 What are the main features of Redux Form?
185 How to add multiple middlewares to Redux?
186 How to set initial state in Redux?
187 How Relay is different from Redux?
188 What is an action in Redux?
React Native
188 What is the difference between React Native and React?
189 How to test React Native apps?
190 How to do logging in React Native?
191 How to debug your React Native?
React supported libraries and Integration
192 What is reselect and how it works?
193 What is Flow?
194 What is the difference between Flow and PropTypes?
195 How to use font-awesome icons in React?
196 What is React Dev Tools?
197 Why is DevTools not loading in Chrome for local files?
198 How to use Polymer in React?
199 What are the advantages of React over Vue.js?
200 What is the difference between React and Angular?
201 Why React tab is not showing up in DevTools?
202 What are styled components?
203 Give an example of Styled Components?
204 What is Relay?
205 How to use TypeScript in create-react-app application?
206 What are the main features of reselect library?
207 Give an example of reselect usage?
209 Does the statics object work with ES6 classes in React?
210 Can Redux only be used with React?
211 Do you need to have a particular build tool to use Redux?
212 How Redux Form initialValues get updated from state?
213 How React PropTypes allow different type for one prop?
214 Can I import an SVG file as react component?
215 Why are inline ref callbacks or functions not recommended?
216 What is render hijacking in React?
217 What are HOC factory implementations?
218 How to pass numbers to React component?
219 Do I need to keep all my state into Redux? Should I ever use react internal state?
220 What is the purpose of registerServiceWorker in React?
221 What is React memo function?
222 What is React lazy function?
223 How to prevent unnecessary updates using setState?
224 How do you render Array, Strings and Numbers in React 16 Version?
225 How to use class field declarations syntax in React classes?
226 What are hooks?
227 What are the rules needs to follow for hooks?
228 How to ensure hooks followed the rules in your project?
229 What are the differences between Flux and Redux?
230 What are the benefits of React Router V4?
231 Can you describe about componentDidCatch lifecycle method signature?
232 In which scenarios error boundaries do not catch errors?
233 Why do not you need error boundaries for event handlers?
234 What is the difference between try catch block and error boundaries?
235 What is the behavior of uncaught errors in react 16?
236 What is the proper placement for error boundaries?
237 What is the benefit of component stack trace from error boundary?
238 What is the required method to be defined for a class component?
239 What are the possible return types of render method?
240 What is the main purpose of constructor?
241 Is it mandatory to define constructor for React component?
242 What are default props?
243 Why should not call setState in componentWillUnmount?
244 What is the purpose of getDerivedStateFromError?
245 What is the methods order when component re-rendered?
246 What are the methods invoked during error handling?
247 What is the purpose of displayName class property?
248 What is the browser support for react applications?
249 What is the purpose of unmountComponentAtNode method?
250 What is code-splitting?
251 What is the benefit of strict mode?
252 What are Keyed Fragments?
253 Does React support all HTML attributes?
254 What are the limitations with HOCs?
255 How to debug forwardRefs in DevTools?
256 When component props defaults to true?
257 What is NextJS and major features of it?
258 How do you pass an event handler to a component?
259 Is it good to use arrow functions in render methods?
260 How to prevent a function from being called multiple times?
261 How JSX prevents Injection Attacks?
262 How do you update rendered elements?
263 How do you say that props are read only?
264 How do you say that state updates are merged?
265 How do you pass arguments to an event handler?
266 How to prevent component from rendering?
267 What are the conditions to safely use the index as a key?
268 Is it keys should be globally unique?
269 What is the popular choice for form handling?
270 What are the advantages of formik over redux form library?
271 Why do you not required to use inheritance?
272 Can I use web components in react application?
273 What is dynamic import?
274 What are loadable components?
275 What is suspense component?
276 What is route based code splitting?
277 Give an example on How to use context?
278 What is the purpose of default value in context?
279 How do you use contextType?
280 What is a consumer?
281 How do you solve performance corner cases while using context?
282 What is the purpose of forward ref in HOCs?
283 Is it ref argument available for all functions or class components?
284 Why do you need additional care for component libraries while using forward refs?
285 How to create react class components without ES6?
286 Is it possible to use react without JSX?
287 What is diffing algorithm?
288 What are the rules covered by diffing algorithm?
289 When do you need to use refs?
290 Is it prop must be named as render for render props?
291 What are the problems of using render props with pure components?
292 How do you create HOC using render props?
293 What is windowing technique?
294 How do you print falsy values in JSX?
295 What is the typical use case of portals?
296 How do you set default value for uncontrolled component?
297 What is your favorite React stack?
298 What is the difference between Real DOM and Virtual DOM?
299 How to add Bootstrap to a react application?
300 Can you list down top websites or applications using react as front end framework?
301 Is it recommended to use CSS In JS technique in React?
302 Do I need to rewrite all my class components with hooks?
303 How to fetch data with React Hooks?
304 Is Hooks cover all use cases for classes?
305 What is the stable release for hooks support?
306 Why do we use array destructuring (square brackets notation) in useState?
307 What are the sources used for introducing hooks?
308 How do you access imperative API of web components?
309 What is formik?
310 What are typical middleware choices for handling asynchronous calls in Redux?
311 Do browsers understand JSX code?
312 Describe about data flow in react?
313 What is react scripts?
314 What are the features of create react app?
315 What is the purpose of renderToNodeStream method?
316 What is MobX?
317 What are the differences between Redux and MobX?
318 Should I learn ES6 before learning ReactJS?
319 What is Concurrent Rendering?
320 What is the difference between async mode and concurrent mode?
321 Can I use javascript urls in react16.9?
322 What is the purpose of eslint plugin for hooks?
323 What is the difference between Imperative and Declarative in React?
324 What are the benefits of using typescript with reactjs?
325 How do you make sure that user remains authenticated on page refresh while using Context API State Management?
326 What are the benefits of new JSX transform?
327 How does new JSX transform different from old transform?
328 How do you get redux scaffolding using create-react-app?

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