React Interview Questions

React is a JavaScript library that makes building user interfaces easy. It was developed by Facebook.

React was first released on March 2013.

Facebook widely uses flux architecture concept for developing client-side web applications. It is not a framework or a library. It is simply a new kind of architecture that complements React and the concept of Unidirectional Data Flow.

Redux has a feature called 'Store' which allows you to save the application's entire State at one place. Therefore all it's component's State are stored in the Store so that you will get regular updates directly from the Store. The single state tree helps you to keep track of changes over time and debug or inspect the application.

Stateless components are pure functions that render DOM-based solely on the properties provided to them.

Popular animation package in React ecosystem are

• React Motion
• React Transition Group

A dispatcher is a central hub of app where you will receive actions and broadcast payload to registered callbacks.

A higher-order component also shortly known as HOC is an advanced technique for reusing component logic. It is not a part of the React API, but they are a pattern which emerges from React’s compositional nature.

Props mean properties, which is a way of passing data from parent to child. We can say that props are just a communication channel between components. It is always moving from parent to child component.

The yield catchphrase is utilized to delay and resume a generator work, which is known as yield catchphrase.

The super keyword helps you to access and call functions on an object’s parent.

A presentational part is a segment which allows you to renders HTML. The segment’s capacity is presentational in markup.

A callback function should be called when setState has finished, and the component is rerendered.

Jest is a JavaScript unit testing framework created by Facebook based on Jasmine. It offers automated mock creation and a jsdom environment. It is also used as a testing component. 

React Router is a routing library which allows you to add new screen flows to your application, and it also keeps URL in sync with what’s being shown on the page.

Here, are important features of React.

• Allows you to use 3rd party libraries
• Time-Saving 
• Faster Development
• Simplicity and Composable
• Fully supported by Facebook.
• Fully supported by Facebook.
• React Components

It is a function which returns an action object. The action-type and the action data are always stored in the action object. Actions can send data between the Store and the software application. All information retrieved by the Store is produced by the actions.

Redux is a library used for front end development. It is a state container for JavaScript applications which should be used for the applications state management. You can test and run an application developed with Redux in different environments. 

• Integrating React with the MVC framework like Rails requires complex configuration.
• React require the users to have knowledge about the integration of user interface into MVC framework.

No, It uses JSX, which is similar to HTML.

Two types of react Components are:

• Function component
• Class component

It is an object which decides how a specific component renders and how it behaves. The state stores the information which can be changed over the lifetime of a React component.

The arrow function helps you to predict the behavior of bugs when passed as a callback. Therefore, it prevents bug caused by this all together.

The main difference the two is that the State is mutable and Pros are immutable.

There are mainly two sorts of information that control a segment: State and Props

• State: State information that will change, we need to utilize State.
• Props: Props are set by the parent and which are settled all through the lifetime of a part. 

Keys allow you to provide each list element with a stable identity. The keys should be unique. 

Error boundaries help you to catch Javascript error anywhere in the child components. They are most used to log the error and show a fallback UI.

StrictMode allows you to run checks and warnings for react components. It runs only on development build. It helps you to highlight the issues without rendering any visible UI.

React context helps you to pass data using the tree of react components. It helps you to share data globally between various react components.

Babel, is a JavaScript compiler that converts latest JavaScript like ES6, ES7 into plain old ES5 JavaScript that most browsers understand.

Here are the major challenges you will face while handling MVC architecture:

• DOM handling is quite expensive
• Most of the time applications were slow and inefficient
• Because of circular functions, a complex model has been created around models and ideas

The reduction is an application method of handling State.

If your element does a stage or lifetime cycle, we should use top-class elements.

When a component's state or props change then rest will compare the rendered element with previously rendered DOM and will update the actual DOM if it is needed. This process is known as reconciliation.

You can’t update props in react js because props are read-only. Moreover, you can not modify props received from parent to child.

You can use forceUpdate() function for re-rending any component. 

Using the State, we can share the data.

It is actually a cross-browser wrapper around the browser’s native event. These events have interface stopPropagation() and preventDefault().

At that time a multi-line JSX expression is the only option left for you.

If you want the browser to read JSX, then that JSX file should be replaced using a JSX transformer like Babel and then send back to the browser.

Webpack in basically is a module builder. It is mainly runs during the development process. 

Portal allows you to render children into a DOM node. CreatePortalmethod is used for it.

Empty tags are used in React for declaring fragments.

Children props are used to pass component to other components as properties. You can access it by using

[crayon-5f30160522ee5038184473/]

'create-react-app' is a command-line tool which allows you to create one basic react application.

Pure components are the fastest components which can replace any component with only a render(). It helps you to enhance the simplicity of the code and performance of the application.

Important lifecycle steps of React js are:

• Initialization
• State/Property updates
• Destruction are the lifecycle of React

A state can be updated on the component directly or indirectly.

Synthetic event is a kind of object which acts as a cross-browser wrapper around the browser’s native event. It also helps us to combine the behaviors of various browser into signal API.

Restructuring is extraction process of array objects. Once the process is completed, you can separate each object in a separate variable.