React Js interview questions

What is React?

React is an open-source Javascript library developed by Facebook Engineers for building complex and interactive User Interfaces in web & mobile applications.

How is React different?

Since React is a little small concentrated on building UI components, it is essentially not the same as a considerable measure of other JavaScript frameworks.

For instance, AngularJS (1.x) approaches building an application by expanding HTML markup and infusing different develops (e.g. Directives, Controllers, Services) at runtime. Subsequently, AngularJS is extremely obstinate about the more architecture design of your application — these reflections are absolutely helpful now and again, yet much of the time, they come at the cost of adaptability.

Why ReactJS is used?

React is used to handle the view part of Mobile application and Web application.

How ReactJS framework is different as compared to others?

Basically, ReactJS is a limited library that builds UI parts, it is essentially not quite the same as a considerable measure of other JavaScript structures. One common example is AngularJS approaches building an app simply by expanding HTML markup and infusing different develop such as controller at runtime. Therefore, AngularJS is exceptionally obstinate about the more noteworthy engineering of your application.

Does ReactJS use HTML?

No, It uses JSX which is simiar to HTM.

What do you know about the component lifecycle in ReactJS?

Component lifecycle is an essential part of this platform. Basically, they have lifecycle events that fall in the three prime categories which are property updates, Initialization and third are Destruction. They are generally considered as a method of simply managing the state and properties of every reach component.

What do you mean by ReactJS?

It is nothing but a JavaScript library which was developed by the popular social media giant facebook. The prime aim was to build user interfaces. The good thing is that developers can simply create renewable UI components. There are certain factors that have contributed to its success and the one among them is the support of a very large community.

What are the life Cycle of ReactJS?

1. Initialization
2. State/Property Updates
3. Destruction

When ReactJS released?

March 2013

How is ReactJs different from AngularJS?

The first difference between both of them is their code dependency. ReactJS depends less to the code whereas AngularJS needs a lot of coding to be done. The packaging on React is quite strong as compared to the AngularJS. Another difference is React is equipped with Virtual Dom while the Angular has a Regular DOM. ReactJS is all about the components whereas AngularJS focus mainly on the Models, View as well as on Controllers. AngularJS was developed by Google while the ReactJS is the outcome of facebook. These are some of the common differences between the two.

What do you mean by Redux?

Many times there is a need to handle the data of an app in a reliable manner. For such tasks, Redux is used. It accurately performs its task and always makes sure that the entire data has been controlled. It is also possible to apply filters in case only a specific part of data is required.

What do you know about Flux?

Basically, Flux is a basic illustration that is helpful in maintaining unidirectional data stream.  It is meant to control construed data unique fragments to make them interface with that data without creating issues. Flux configuration is insipid; it’s not specific to React applications, nor is it required to collect a React application.  Flux is basically a straightforward idea, however in you have to exhibit a profound comprehension of its usage.

What is current stable version of ReactJS?

Version: 15.5
Release on: April 7, 2017

What is Repository URL of ReactJS?

https://github.com/facebook/react

What is JSX?

It is basically a novel dialect of the popular JavaScript that simply integrates the HTML templates into the code of JavaScript. The browser is not capable to read the code simply and thus there is a need for this integration. Generally, WebPack or Babel tools are considered for this task. It has become a very popular approach in the present scenario among the developers.

Do you think ReactJS has any limitations? If so, tell a few?

Yes, there are a few drawbacks which are associated with this platform. The leading drawback of the ReactJS is the size of its library. It is very complex and creates a lot of confusion among the developers. Also, there are lots of developers all over the world which really don’t like the JSX and inline templating. In addition to this, there is another major limitation of ReactJS and i.e. only cover one layer of the app and i.e.View. Thus to manage the development, developers have to depend on several other technologies which consume time.

What are the feature of ReactJS?

1. JSX
2. Components
3. One direction flow (Unidirectional Flux)

What are the Advantages of ReactJS?

 Uses virtual DOM which is JavaScript object which will improve apps performance.
 Can be used on client and server side
 Component and Data patterns improve readability.
 Improves SEO Performance
 Can be used with other framework also.

How the parent and child components exchange information?

This task is generally performed with the help of functions. Actually, there are several functions which are provided to both parent and child components. They simply make use of them through props. Their communication should be accurate and reliable. The need of same can be there anytime and therefore functions are considered for this task. They always make sure that information can be exchanged easily and in an efficient manner among the parent and child components.

Give one basic difference between pros and state?

Pros are immutable while the state is mutable. Both of them can update themselves easily.

How do you tell React to build in Production mode and what will that do?

Ordinarily you’d utilize Webpack’s DefinePlugin strategy to set NODE_ENV to production. This will strip out things like propType approval and additional notices. Over that, it’s likewise a smart thought to minify your code in light of the fact that React utilizes Uglify’s dead-code end to strip out advancement just code and remarks, which will radically diminish the measure of your package.

What do you understand with the term polling?

The server needs to be monitored to for updates with respect to time. The primary aim in most of the cases is to check whether novel comments are there or not. This process is basically considered as pooling. It checks for the updates approximately after every 5 seconds. It is possible to change this time period easily. Pooling help keeping an eye on the users and always make sure that no negative information is present on the servers. Actually, it can create issues related to several things and thus pooling is considered.

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

If your component has state or a lifecycle method(s), use a Class component. or else, use a Functional component.

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