Useful React Js Interview Question Part 1

What is React?

React is an open-source JavaScript library developed by facebook Engineers for constructing complicated and interactive consumer Interfaces in web & mobile programs.

How is React different?

React is a bit small focused on constructing UI components, it is largely now not similar to a giant degree of other JavaScript frameworks.

As an example, AngularJS (1.x) techniques building an software by increasing HTML markup and infusing specific develops (e.g. Directives, Controllers, services) at runtime. Eventually, AngularJS is extraordinarily obstinate about the greater structure design of your utility β€” these reflections are absolutely useful on occasion, yet lots of the time, they arrive on the price of adaptability.

Why ReactJS is used?

React is used to handle the view a part of mobile utility and web utility.

How ReactJS framework is different as compared to others?

Essentially, ReactJS is a limited library that builds UI components, it is essentially not quite similar to a significant measure of different JavaScript structures. One commonplace instance is AngularJS techniques building an app simply through increasing HTML markup and infusing specific develop which includes controller at runtime. Consequently, AngularJS is highly obstinate about the extra noteworthy engineering of your software.

Does ReactJS use HTML?

No, It makes use of JSX which is simiar to HTM.

What do you understand about the component lifecycle in ReactJS?

Component lifecycle is a crucial part of this platform. essentially, they’ve lifecycle events that fall within the three top classes which can be property updates, Initialization and third are Destruction. they are normally taken into consideration as a method of clearly dealing with the state and properties of every reach thing.

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?

  • Initialization
  • State/Property Updates
  • Destruction

When ReactJS released?

March 2013

How is ReactJs different from AngularJS?

The first difference between both of them is their code dependency. ReactJS relies upon much less to the code whereas AngularJS wishes a lot of coding to be performed. The packaging on React is pretty strong 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 specifically on the models, View as well as on Controllers. AngularJS become developed through Google while the ReactJS is the outcome of facebook. These are a number of the common variations among the two.

What do you mean by Redux?

In many instances there’s a need to deal with the information of an app in a reliable way. For such obligations, Redux is used. It correctly plays its project and usually makes certain that the whole records have been managed. It’s also possible to apply filters in case most effective a particular a part of data is required.

What do you know about Flux?

Essentially, Flux is a basic example this is useful in keeping unidirectional data stream. It is supposed to govern construed data unique fragments to lead them to interface with that records without developing issues. Flux configuration is insipid; it is no longer particular to React applications, neither is it required to collect a React software. Flux is basically an honest idea, however in you have to show off 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?

What is JSX?

It is largely a novel dialect of the famous JavaScript that simply integrates the HTML templates into the code of JavaScript. The browser isn’t always capable to study the code truly and therefore there may be a need for this integration. Usually, WebPack or Babel tools are considered for this assignment. It has become a very popular method within the present scenario a number of developers.

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

Yes, there are some drawbacks which might be related to this platform. The main disadvantage of the ReactJS is the scale of its library. It’s far very complicated and creates quite a few confusion most of the builders. Also, there are plenty of developers everywhere in the world which genuinely don’t like the JSX and inline templating. Similarly to this, there’s every other foremost challenge of ReactJS and that i.e. best cover one layer of the app and that i.e.View. Therefore to control the development, developers have to rely upon several different technologies which consume time.

What are the feature of ReactJS?



One direction flow (Unidirectional Flux)

What are the Advantages of ReactJS?

Makes use of virtual DOM that is JavaScript item with a view to improve apps overall performance

Can be used on client and server side

Component and Data patterns improve readability.

Improves SEO overall Performance.

Can be used with other framework also.

How the parent and child components exchange information?

This task is commonly executed with the help of features. Genuinely, there are several functions which can be supplied to both parent and child components. They definitely employ them via props. Their communication should be accurate and dependable. The want of same can be there anytime and therefore features are taken into consideration for this task. They always make sure that records may be exchanged easily and in an efficient manner some of 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 replace themselves without difficulty.

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

Ordinarily you would make use of Web packs DefinePlugin strategy to set NODE_ENV to production. This will strip out things like propType approval and further notices. Over that, it is likewise a clever idea to minify your code in mild of the reality that Reacts makes use of Uglify’s useless-code quit to strip out advancement just code and remarks, for you to considerably lessen the measure of your bundle.

What do you understand with the term polling?

The server desires to be monitored for updates with admire to time. The primary intention in most of the instances is to test whether novel remarks are there or not. This technique is essentially considered as pooling. It checks for the updates approximately every 5 seconds. It is possible to trade this time period easily. Pooling help keeping a watch at the users and constantly make sure that no negative facts are a gift on the servers. In reality, it could create problems related to numerous matters and for that reason 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.

What do you mean by virtual DOM?

For all the available DOM objects in ReactJS, there may be a parallel virtual DOM item. it is nothing but may be considered as the lighter model of the true replica and is robust in getting rid of the complex code. It is also used as a Blue Print for appearing several primary experiments. Many developers additionally use it while practicing this technology.

Compare MVC with Flux?

MVC methods are currently considered as outdated. although they are successful to deal with statistics issues, controllers as well as UI, many builders found that it doesn’t properly work while applications size will increase. But, they may be capable to deal with some of the important thing issues inclusive of removing the shortage of facts integrity in addition to handling the information waft which isn’t always well described. On the other side, Flux works flawlessly with all of the sizes irrespective of their length.

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

Basically, a React element describes what you want to look at the screen. no longer all that essentially, a React detail is a protest portrayal of some UI.

A React factor is a function or a category which instead acknowledges input and returns a React factor (ordinarily by means of JSX which receives transpired to a createElement invocation).

Tell us three reasons behind the success of ReactJS?

ReactJS is a technology that may be trusted for complex obligations. Even as performing any project thru it, developers need no longer worry about the bugs. It constantly ensures error-free effects and the excellent part is it gives scalable apps. It’s far very rapid technology and might simply be trusted for first-rate outcomes.

In which lifecycle event do you make AJAX requests and why?

AJAX solicitations ought to move inside the componentDidMount lifecycle event.

There are more than one reasons behind this,

Fiber, the following utilization of React’s reconciliation algorithm, will be capable of beginning and end rendering as required for execution advantages. One of the trade-offs of that is componentWillMount, the other lifecycle event where it may bode nicely to influence an AJAX to ask for could be “non-deterministic”. This indicates React can also begin calling componentWillMount at special occasions at on every occasion point it senses that it desires to. This would certainly be a terrible system for AJAX requests.

You cannot make sure the AJAX request may not clear up before the issue mounts. In the event that it did, that could imply which you’d be attempting to setState on an unmounted issue, which won’t work, as well as React will holler at you for. Doing AJAX in componentDidMount will make certain that there is an aspect to replace.

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