Top 100+ React Native Interview Questions And Answers
Question 1. What Is React Native?
Answer :
React Native is the subsequent generation of React - a Javascript code library developed through Facebook and Instagram, which turned into released on Github in 2013. Native app introduction approach writing apps for a selected running device.
React Native enables builders reuse code across the net and on cell. Engineers may not should construct the identical app for iOS and for Android from scratch - reusing the code across each running system.
Android and iOS have very distinctive codebases and startups and businesses regularly struggle to hire - or have the funds for- engineers for both. Now simply one developer can write across one-of-a-kind cell operating systems.
Question 2. Why Open Source?
Answer :
"If we work together within the open, we are able to advance the nation of technology together," Facebook said in a weblog post the previous day evening.
Altruism aside, opting to open source code is a intricate choice. Keeping a groups infrastructure below-wraps has commercial advantages, specifically whilst your generation is your business version.
But the developer network is loyal to people who open up. Web engineers internationally are short to factor out a computer virus in the code without cost.
Developing open supply tasks enables keep Facebook one of the most coveted agencies to work for. Developers want a project, and a sense of giving back - and Facebook desires a large pool of gifted engineers to pick its personnel from.
Plus, it saves on training. If each engineer Facebook hires already knows a way to write in React Native, they've a strolling begin.
Facebook has a way of life of maturing its development. Over ten years' it has scaled to serve a thousand million customers, lots of builders and 3 most important platforms - iOS, Android and Web.
It's a giant development from when the fledgling startup copied Facebook code on Harvard University's server for releases and,"poke on it to look if it turned into still running each day at 10am," mobile engineering manager Bryan O'Sullivan joked earlier this yr.
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Question three. How Did Facebook Write React Native For Android?
Answer :
The first cross-platform React Native app - advertisements supervisor - turned into advanced by means of the London-based dev group, who have been inside the US to announce the Android launch the previous day nighttime. Ads supervisor lets businesses that put it up for sale on the social community manage their debts and create new ads.
React Native has only these days been validated in manufacturing and building a new app primarily based at the framework carried a few chance.
Three product engineers acquainted with React set approximately to create an app for Android and expected problems with the good judgment necessary to recognize differing time zones, date formats, currencies and advert codecs across the world.
This enterprise good judgment changed into already written in JavaScript, and the team knew it wouldn't be green to construct all of it once more in Objective-C to do it once more in Java for Android.
Now this assignment has been launched on Github, developers can use a single workflow to increase for iOS and Android. This manner you may use the same editor and propagate it to each the iOS simulator and Android emulator at the same time.
Question four. What's The Challenges With React Native?
Answer :
Working throughout separate iOS and Android codebases is hard.
"When we were constructing the app, Facebook used this model, and all our construct automation and developer techniques had been installation round it. However, it doesn't work well for a product that, for the maximum part, has a unmarried shared JavaScript codebase," wrote Daniel Witte and Philipp von Weitershausen, engineers at Facebook in a weblog the day past.
Developers who regularly struggle to determine out in which the grasp code exists and whether bugs were constant in all structures may want to hold out for whilst Facebook opens up its unified repository. It is moving all of its code from Git to Mercurial, and can be one of the largest codebases of its type.
Google is every other net large that understands the energy of open supply, recently committing to OpenStack and growing an enitrely open source box management assignment, Kubernetes. The task seems at odds with its very own Google cloud business, however once more, it is aware of that the blessings outweigh any lack of Google cloud customers.
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Question 5. Advantages Of React Native?
Answer :
The fact that React Native simply renders using its host platform's wellknown rendering APIs allows it to face out frommost existing techniques of go-platform utility developement ,like Cordova or Ionic. Existing methods of writing cell packages using combos of JavaScript,HTML,and CSS normally render the usage of webviews.While this approach can paintings, it also comes with drawbacks,specially round performance.
Additionally,they do now not commonly have get entry to to the host platform's set of native UI elements.When those frame works do try and mimic local UI factors,the results typically "feel" just a little off; reverse-engineering all the excellent details of things like animations takes an huge amount of effort,and they could speedy become obsolete.
In contrast, Reactive Native truly interprets your markup to real,local UI factors,leveraging present means of rendering views of whatever platform you are working with. Additionally,React works one after the other from the primary UI thread,so your software can maintain high performance with out sacrificing capability.The update cycle in React Native is similar to in React :while props or state change,React Native re-renders the perspectives.The major differnce between React Native and React within the browser is that React Native does this by leveraging the UI libraries of its host platform, in preference to using HTML and CSS markup.
For developers familiar with running on the Web with React,this means you may write cell apps with performance and look and sense of anative utility,at the same time as using familiar equipment. React Native additionally represents an development over normal cellular development in two other regions:the developer enjoy and pass-platform development ability.
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Question 6. How To Handling Multiple Platforms?
Answer :
React Native gracefully handles a couple of systems. The massive majority of the React Native APIs are go-platform, so you simply need to jot down one React Native thing, and it's going to paintings seamlessly on each iOS and Android. Facebook claims that their Ad Manager utility has 87% code reuse across the 2 platforms, and I wrote a flashcard app with none platform-particular code in any respect.
If you do need to write down platform-particular code -- due to exceptional interplay tips on iOS and Android, as an example, or due to the fact you want to take advantage of a platform-unique API -- it truly is clean, too. React Native permits you to specify platform-particular versions of every aspect, which you can then combine into the relaxation of your React Native utility.
Question 7. React Native - Differences Between Android And Ios?
Answer :
The base setup for constructing with Android and iOS are the identical, however once you start moving into the improvement of your app, there are some differences. From what I've experienced, we can in all likelihood wager on the use of approximately 80% of our code go platform. I've heard of others the use of up to 90%, and I've typically heard the range being round eighty five%.
To use the code move platform, you would simply copy the code out of your .Ios.Js or .Android.Js report, and replica it into the opposite. As long as there aren't platform particular components, it must paintings.
Also:
There are some modules that have been build especially for iOS, and there are a few that had been specially built for Android, and some of them paintings cross platform. For example, ActivityIndicatorIOS is an iOS styled element, but if you look inside the factor itself, you may see each ActivityIndicatorIOS.Android.Js and ActivityIndicatorIOS.Ios.Js, so it must as a minimum paintings move platform, but UI will probable not be what you will be seeking out in Android.
If you put in any plugins that need to access any native functionality, as an instance the usage of a custom font, you may need to do a bit of work one after the other (on each platform) to get them running for every platform and it'll now not work pass platform.
Bridging may be absolutely distinctive for each platform, even though this can not be some thing you will even ought to fear about until you had to do something that React Native does no longer assist out of the container. To construct in IOS, you will need a Mac and Xcode. To construct in Android, you'll need the android SDK and some type of emulator (I use Genymotion). But understand that as of now, you can't broaden iOS on a Windows system until you operate something like ExponentJS, however if you have a Mac, you may broaden go platform.
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Question eight. Are All React Components Usable In React Native?
Answer :
Web React components use DOM factors to show (ex. Div, h1, desk, and many others) but these aren't supported by React Native. You'll need to find libraries/components made mainly for React Native.
I doubt there are components that helps each, consequently it must be fairly clean to determine out if it is made for React Native or no longer. As of now, if the writer does not particularly say that they made for React Native, it possibly does now not work on React Native.
Question 9. Passing Functions Between Components In React And React Native?
Answer :
I could stay away from such passing features between additives. I continually use Flux structure with ReactJs and React Native.
Keep components just to render stuff by residences and sending new movements.
You have hard dependency between additives. This stuff does now not scale. It might be hard to maintaine such code.
What i for my part do is simply write moves, stores, dispatcher and don't use any dependency on stuff like redux, due to the fact React Native is envolving rapidly and you in no way realize in case your dependencies will do it at same velocity.
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Question 10. Difference Between React Native And Nativescript, Which One Do You Prefer And Why?
Answer :
React JS for the net is tremendous. But in relation to React Native - i felt i was boxed or caged to Reacts manner of creating the views and building the display there after.
With NativeScript it really is not the case. The UI definition follows XML syntax. I know XML so smooth to follow. When it involves application good judgment - it lets in ES5, TypeScript - again which i already know so i can reuse my talent. You use a subset of CSS to fashion your app. Again huge plus point here - if you know CSS3, NS lets in you to apply maximum of the basic rule sets to fashion your app. Basically NS is all approximately open standards - you don't must examine whatever new. You operate what you all ready recognize.
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Question 11. Are There Any Disadvantages To Using React Native For Mobile Development?
Answer :
Having performed around with it for a few weeks, I've found React Native to be pretty buggy. I don't suppose it's everywhere close to production ready. A lot of capabilities are currently nonetheless lacking, as an example, pin annotations for maps. Being that it's open supply, there may be nothing preventing you from constructing the function yourself, but in case you're trying to get something created quickly / for production, you're higher off using developing at once for iOS or Android.
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Question 12. What Is The Difference Between Using Constructor Vs Getinitialstate In React / React Native?
Answer :
The strategies are not interchangeable. You have to initialize kingdom inside the constructor whilst the use of ES6 training, and outline the getInitialState technique while the usage of React.CreateClass.
Elegance MyComponent extends React.Component
constructor(props)
exquisite(props);
this.Country = /* initial nation */ ;
is equivalent to
var MyComponent = React.CreateClass(
getInitialState()
go back /* preliminary kingdom */ ;
,
);
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Question 13. Re-render On Changes?
Answer :
In addition to props, components can also have an internal state. The most outstanding example of that behavior might be a click counter that updates its cost whilst a button is pressed. The wide variety of clicks itself might be stored within the nation.
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Question 14. What Is A Prop?
Answer :
A right analogy to outline "what's a prop?" has been likened to the real existence scenario of while someone movements from one domestic to some other. A shifting van pulls up and all of the contents of the home are loaded in the van and it drives off to be unloaded into the new residence. The residence is the surroundings. The surroundings includes the actual walls, flooring, ceilings, doorways- the structure of the residence. This does not move. It is desk bound and permanent. The objects boxed up, protected in pads, and achieved to the moving van whilst someone is converting residences would all be taken into consideration the props.
Question 15. What Happens When You Call Setstate?
Answer :
The first component React will do when setState is referred to as is merge the object you surpassed into setState into the modern country of the element. This will kick off a technique known as reconciliation. The stop goal of reconciliation is to, inside the maximum green manner possible, update the UI primarily based in this new country.
To do that, React will assemble a brand new tree of React factors (which you can think about as an item representation of your UI). Once it has this tree, so one can figure out how the UI have to exchange in response to the new kingdom, React will diff this new tree in opposition to the previous detail tree. By doing this, React will then recognise the precise changes which took place, and by using understanding precisely what changes passed off, will capable of minimize its footprint at the UI by using simplest making updates in which certainly important.
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Question sixteen. What’s The Difference Between An Element And A Component In React?
Answer :
Simply positioned, a React element describes what you want to look at the display. Not so surely positioned, a React element is an object illustration of some UI.
A React aspect is a characteristic or a class which optionally accepts enter and returns a React detail (normally thru JSX which receives transpiled to a createElement invocation).
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Question 17. When Would You Use A Class Component Over A Functional Component?
Answer :
If your thing has state or a lifecycle technique(s), use a Class issue. Otherwise, use a Functional factor.
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Question 18. What Are Refs In React And Why Are They Important?
Answer :
Refs are an get away hatch which assist you to get direct access to a DOM element or an instance of a component. In order to use them you upload a ref characteristic for your element whose price is a callback feature with a view to receive the underlying DOM element or the set up example of the factor as its first argument.
Magnificence UnControlledForm extends Component
handleSubmit = () =>
console.Log("Input Value: ", this.Input.Price)
render ()
return (
<form onSubmit=this.HandleSubmit>
<input
type='text'
ref=(input) => this.Input = input />
<button type='submit'>Submit</button>
</form>
)
Above be aware that our enter field has a ref attribute whose fee is a feature. That function receives the actual DOM element of input which we then placed on the example which will have get entry to to it interior of the handleSubmit feature.
It’s often misconstrued that you want to apply a class thing in an effort to use refs, but refs can also be used with practical components with the aid of leveraging closures in JavaScript.
Characteristic CustomForm (handleSubmit)
permit inputElement
return (
<form onSubmit=() => handleSubmit(inputElement.Fee)>
<input
type='text'
ref=(input) => inputElement = input />
<button type='submit'>Submit</button>
</form>
)
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Question 19. What Are Keys In React And Why Are They Important?
Answer :
Keys are what help React keep song of what objects have modified, been brought, or been removed from a listing.
Render ()
go back (
<ul>
this.Country.TodoItems.Map((assignment, uid) =>
return <li key=uid>challenge</li>
)
</ul>
)
It’s critical that each key be unique amongst siblings. We’ve talked some instances already approximately reconciliation and a part of this reconciliation method is appearing a diff of a brand new detail tree with the most preceding one. Keys make this system greater efficient whilst dealing with lists due to the fact React can use the key on a baby detail to speedy recognise if an element is new or if it was simply moved whilst comparing timber. And no longer only do keys make this method more efficient, but with out keys, React can’t understand which local country corresponds to which item on move. So never forget keys when mapping.
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Question 20. What Is The Difference Between A Controlled Component And An Uncontrolled Component?
Answer :
A massive a part of React is this concept of having components control and manipulate their personal state. What occurs while we throw local HTML shape factors (enter, choose, textarea, etc) into the mixture? Should we've React be the “single source of reality” like we’re used to doing with React or have to we allow that form facts to live in the DOM like we’re used to normally doing with HTML shape factors? These two questions are at the coronary heart of controlled vs out of control additives.
A controlled issue is a part where React is in control and is the single supply of reality for the shape records. As you may see below, usernamedoesn’t live inside the DOM however rather lives in our element kingdom. Whenever we want to update username, we call setState as we’re used to.
Class ControlledForm extends Component
country =
username: ''
updateUsername = (e) =>
this.SetState(
username: e.Target.Cost,
)
handleSubmit = () =>
render ()
return (
<form onSubmit=this.HandleSubmit>
<input
type='text'
value=this.State.Username
onChange=this.UpdateUsername />
<button type='submit'>Submit</button>
</form>
)
An out of control aspect is where your shape data is handled with the aid of the DOM, rather than interior your React thing.
You use refs to perform this.
Class UnControlledForm extends Component
handleSubmit = () =>
console.Log("Input Value: ", this.Input.Fee)
render ()
go back (
<form onSubmit=this.HandleSubmit>
<input
type='text'
ref=(input) => this.Input = enter />
<button type='submit'>Submit</button>
</form>
)
Though uncontrolled additives are normally simpler to put into effect since you just seize the price from the DOM using refs, it’s normally recommended that you favor managed components over uncontrolled additives. The most important reasons for this are that managed additives guide instant subject validation, will let you conditionally disable/permit buttons, put in force enter codecs, and are extra “the React way”.
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Question 21. In Which Lifecycle Event Do You Make Ajax Requests And Why?
Answer :
AJAX requests must cross in the componentDidMount lifecycle event.
There are a few reasons for this,
Fiber, the following implementation of React’s reconciliation algorithm, may have the capacity to start and forestall rendering as needed for performance benefits. One of the trade-offs of this is that componentWillMount, the opposite lifecycle occasion in which it might make sense to make an AJAX request, may be “non-deterministic”. What this means is that React may also begin calling componentWillMount at numerous times every time it feels like it wishes to. This could manifestly be a awful formula for AJAX requests.
You can’t assure the AJAX request gained’t remedy before the component mounts. If it did, that might suggest which you’d be looking to setState on an unmounted thing, which no longer only won’t work, however React will yell at you for. Doing AJAX in componentDidMount will assure that there’s a aspect to replace.
Question 22. What Does Shouldcomponentupdate Do And Why Is It Important?
Answer :
Above we pointed out reconciliation and what React does whilst setState is called. What shouldComponentUpdate does is it’s a lifecycle technique that allows us to choose out of this reconciliation technique for positive additives (and their child additives). Why would we ever want to do that? As noted above, “The quit goal of reconciliation is to, inside the most efficient manner feasible, update the UI based on new nation”. If we recognize that a sure phase of our UI isn’t going to change, there’s no reason to have React go through the problem of trying to parent out if it must. By returning fake from shouldComponentUpdate, React will count on that the modern component, and all its child additives, will live the same as they presently are.
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Question 23. How Do You Tell React To Build In Production Mode And What Will That Do?
Answer :
Typically you’d use Webpack’s DefinePlugin technique to set NODE_ENV to manufacturing. This will strip out things like propType validation and additional warnings. On top of that, it’s also a terrific idea to minify your code because React makes use of Uglify’s dead-code removal to strip out improvement simplest code and remarks, so one can considerably lessen the scale of your package.
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Question 24. Describe How Events Are Handled In React?
Answer :
In order to resolve cross browser compatibility troubles, your event handlers in React could be surpassed times of SyntheticEvent, that's React’s move-browser wrapper around the browser’s native occasion. These synthetic occasions have the identical interface as local events you’re used to, besides they work identically across all browsers.
What’s mildly exciting is that React doesn’t honestly attach occasions to the kid nodes themselves. React will pay attention to all events at the pinnacle degree using a single occasion listener. This is right for performance and it additionally method that React doesn’t need to fear about keeping music of event listeners whilst updating the DOM.
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Question 25. What Is The Difference Between Createelement And Cloneelement?
Answer :
createElement is what JSX receives transpiled to and is what React uses to create React Elements (item representations of a few UI). CloneElement is used which will clone an element and skip it new props.
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Question 26. What Is The Second Argument That Can Optionally Be Passed To Setstate And What Is Its Purpose?
Answer :
A callback function a good way to be invoked when setState has finished and the element is re-rendered.
Something that’s not spoken of plenty is that setState is asynchronous, that's why it takes in a 2d callback characteristic. Typically it’s satisfactory to apply every other lifecycle technique in preference to relying on this callback feature, however it’s excellent to realize it exists.
This.SetState(
username: 'tylermcginnis33' ,
() => console.Log('setState has completed and the thing has re-rendered.')
)
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Question 27. What Is Wrong With This Code?
Answer :
return
streak: prevState.Streak + props.Matter
)
Nothing is incorrect with it ????. It’s hardly ever used and now not well known, however you can also skip a characteristic to setState that gets the previous nation and props and returns a new nation, just as we’re doing above. And not only is not anything wrong with it, however it’s also actively endorsed if you’re putting state based on previous nation.
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Question 28. Is React Native Like Other Hybrid Apps Which Are Actually Slower Than Native Mobile Apps?
Answer :
React Native compiles a real cellular and is engineered for excessive performance, an amazing instance of a high overall performance app is Facebook IOS app; it uses React Native and IOS users have a quite appropriate concept of the way smoothly the Facebook app works on IOS gadgets.
Question 29. Do We Use The Same Code Base For Android And Ios?
Answer :
Yes, we use the equal code base for Android and IOS and React take cares of the native additives translations. For instance: A React Native ScrollView uses native UiScrollView on IOS and ScrollView on Android.
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Question 30. Can We Use React Native Code Alongside With React Native?
Answer :
Yes, we are able to use Native code alongside JavaScript to get our obligations done, so the constraints in previous such platforms such as Titanium could be no more.
Question 31. Is React Native A Native Mobile App?
Answer :
Yes, React Native Compiles a local cellular app the use of local app components. It’s neither a Hybrid Mobile app that uses WebView to run the HTML5 app or a cellular internet app. React Native builds a actual mobile app that’s indistinguishable from an app built the usage of Objective-C or Java.
Question 32. What Is The Difference Between React And React Native?
Answer :
ReactJs is a JavaScript Library used for growing apps in HTML5 using JavaScript because the growing language and React Native is used to broaden local mobile apps the use of JavaScript as the development language.
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