CONTUS REACT JS INTERVIEW QUESTIONS

Here is the list React JS Interview Questions which are recently asked in Contus company. These questions are included for both Freshers and Experienced professionals. Our React JS Training has Answered all the below Questions.

1. Give one basic difference between pros and state?

The difference is that state is something like attributes in OOP: it’s something local to a class (component), used to better describe it. Props are like parameters – they are passed to a component from the caller of a component (the parent): as if you called a function with certain parameters.

2. What do you understand with the term polling?

Sometimes when building web applications, you’re going to need to keep track of data being created or updated asynchronously by another service. Polling is one way to accomplish this, and all it is, is simply hitting an API’s endpoint to retrieve any new data at a set interval of time.

3. When would you use a Class Component over a Functional Component?

If you are writing a presentational component which doesn’t have its own state or needs to access a lifecycle hook, use functional component as much as possible. For state management you can use class component.

4. What do you mean by 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 React DOM. They may also be considered a part of “virtual DOM” implementation in React.

5. Compare MVC with Flux?

Flux uses ‘Stores’ to cache any application associated with data or state whereas MVC model attempts to model a single object. MVC doesn’t have the concept of the Store. The Store is more like a model in MVC, but it handles the state of several objects instead of just denoting a single database record.

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6. What’s the difference between an Element and a Component in React?

React Element – It is a simple object that describes a DOM node and its attributes or properties you can say. It is an immutable description object and you can not apply any methods on it.

React Component – It is a function or class that accepts an input and returns a React element.

7. Tell us three reasons behind the success of ReactJS?

React JS simplifies the overall process of scripting components.
It facilitates advanced maintenance and boosts productivity.
It guarantees quicker rendering.

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8. What do you mean by prop?

Props” stands for properties. It is a special keyword in React which is used for passing data from one component to another. Logically, components are just like JavaScript functions. They accept random inputs and return React elements which tell what should be displayed on the screen.

9. What is meant by event handling?

Handling events with React elements is very similar to handling events on DOM elements. React events are named using camelCase, rather than lowercase. With JSX you pass a function as the event handler, rather than a string.

10. What are controlled and uncontrolled components?

In a controlled component, form data is handled by a React component. The alternative is uncontrolled components, where form data is handled by the DOM itself. To write an uncontrolled component, instead of writing an event handler for every state update, you can use a ref to get form values from the DOM.

11. Mention the key benefits of Flux?

Flux is open-source, easy to understand and maintain.
It is more of a design pattern than a formal framework.
It complements React as view and Runtime errors are reduced.
It follows the concept of Unidirectional Data Flow model.

12. What are pure functional Components?

A React component is considered pure if it renders the same output for the same state and props. Pure components have some performance improvements and render optimizations since React implements the shouldComponentUpdate() method for them with a shallow comparison for props and state

13. What happens during the lifecycle of a React component?

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. Mounting is the stage of rendering the JSX returned by the render method itself.

14. What do you know about React Router?

React Router, and dynamic, client-side routing, allows us to build a single-page web application with navigation without the page refreshing as the user navigates. React Router uses component structure to call components, which display the appropriate information

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CONTUS REACT JS INTERVIEW QUESTIONS