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ReactJS Interview Questions and Answers

ReactJS Interview Questions and answers for beginners and experts. List of frequently asked ReactJS Interview Questions with answers by Classicus Infotech. We hope these ReactJS Interview Questions and answers are useful and will help you to get the best job in the networking industry.

Display or Create DOM properties in Reacts ?
Element

Which function is used to display a DOM?
ReactDOM.render()

What are the different types of components?
Function and Class

Different types of DOM?
shadow and Virtual

How to find area of suitability in React?
React Fiber

Which function is used to create UI representation?
React.createElement()

What are the different phases of component lifecycle?
Initialization,Mounting,Updating, UnMounting

What is reconciliation?
When a components props or state change, React decides whether an real DOM update is necessary by comparing the newly returned element with the before rendered one. When they not equal, React will inform the DOM. This process is called reconciliation.

What are fragments?
Its mutual pattern in React which is used for a component to return multiple elements. Fragments let group a list of children without adding extra nodes to the DOM.

What is React DOM Server?
The React DOM Server object enables us to render components to static markup . This object is mostly used for server-side rendering (SSR). The below methods can be used in both the server and browser environments:
renderToString()
renderToStaticMarkup()

What will happen if you use set State() in constructor?
When you use set State(), then apart from assigning to the object state React also re renders the component and all its children. We would get error like this: Can only update a mounted or mounting component. Hence we need to use this. stateto initialize variables inside constructor.

Why is a component constructor called only once?
React’s appeasement algorithm assumes that without any information to the contrary, if a custom component appears in the same place on consequent renders, it’s the same component as before, so reuses the previous instance moderately than making a new one.

What are the popular packages for animation?
React Motion and React Transition Group are popular animation packages in React ecosystem.

What is Redux?
Redux is an expected state container for JavaScript apps based on the Flux design pattern. Redux can be used mutually with React, or with any other view library. It is a little size (about 2kB) and has no dependency.

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