React Native Interview Questions And Answers

Q.1.What Is React Native?
A. React Native is the next generation of React – a Javascript code library developed by Facebook and Instagram, which was released on Github in 2013. Native app creation means writing apps for a specific operating system.React Native helps developers reuse code across the web and on mobile. Engineers won’t have to build the same app for iOS and for Android from scratch – reusing the code across each operating system.Android and iOS have very different codebases and startups and businesses often struggle to hire – or afford- engineers for both. Now just one developer can write across different mobile operating systems.
Q.2.What Is A Prop?
A. good analogy to define “what is a prop?” has been likened to the real life situation of when a person moves from one home to another. A moving van pulls up and all the contents of the home are loaded in the van and it drives off to be unloaded into the new house. The house is the scenery. The scenery includes the actual walls, floors, ceilings, doors- the architecture of the house. This does not move. It is stationary and permanent. The items boxed up, covered in pads, and carried out to the moving van when a person is changing residences would all be considered the props.
Q.3.Differentiate between the React component and the React element.
A. React component is a class or function that accepts input and returns a React element while React element displays the look of React Component Instance to be created.
Q.4.Explain the difference between ReactJs and React Native?
A. The ReactJs is JavaScript library to develop apps in HTML5 while using JavaScript as the developing language. Whereas, React Native is a JavaScript framework used to create native mobile applications while using JavaScript as the development language.
Q.5.What does prop mean in Native React?
A. The ReactJs is JavaScript library to develop apps in HTML5 while using JavaScript as the developing language. Whereas, React Native is a JavaScript framework used to create native mobile applications while using JavaScript as the development language.
Q.6.Explain HOC.
A. Higher Order Component, shortly known as HOC is an advanced React Native technique to reuse the component logic. The function obtains a component and returns a new element.
Q.7.Why React Native has very clear animations?
A. The animated API of Native React is designed to be serialized. That means users can send animation to native without having to go through the bridge on every frame. Once the animation gets started, the JS thread will be blocked, and the animation will run smooth. Due to the code is converted to native views before rendering, the animation will run smoothly in React native
Q.8.What do you understand from “In React, everything is a component.”
A. Components are the building blocks of a React application’s UI. These components split up the entire UI into small independent and reusable pieces. Then it renders each of these components independent of each other without affecting the rest of the UI.
Q.9.Is it possible to use the same code base for both Android and iOS in React Native?
A. Yes, it’s entirely possible. App developers use the same code base for iOS and Android as Reacts entirely takes care of the native components translations part. For example, a React Native ScrollView uses ScrollView on Android and native UiScrollView on IOS.
Q.10.What is react native and why it is used?
A. React Native is a next-generation JavaScript code library developed by Facebook for native app creation. The feature of reusable code across the web and mobile devices makes React Native highly demanding among developers. With the reusable codes, app developers don’t have to build the same app for different platforms from scratch.
Q.11.What are the limitations with React native?
A. The React Native has following limitations or cons

  • Security risks
  • Single threaded interface
  • Poor memory management
  • Doesn’t support all native APIs
  • Dependable on third-party libraries
  • Not equivalent to true native apps written entirely on Java or Swift/Obj-C.
Q.12.Who is using react native?
A. Today hundreds and thousands of mobile applications are using React native as their base. Many multi-billion companies are also using this framework for their business apps, such as Facebook, Uber, Instagram, Wal-Mart, Skype, Pinterest, Tencent QQ,,, Adidas GLITCH, JD, Baidu Mobile and more.
Q. 13.What do you mean by redux in react native?
A. Redux is a standalone state management library present in React Native and can be used combined with any framework or library. With the use of Redux, app developers can use one application state as a global state and interact with the state from any react component will be easy.
Q. 14.What is virtual Dom and how it is work in react native?
A. Virtual DOM is a copy of the real DOM. This node tree lists the elements, their attributions, contents, and properties also. Whenever any underlying data changes in React Native, the entire UI will be re-rendered in Virtual DOM representation. Then, the difference between previous DOM representation and virtual DOM will be counted. After that, the real DOM will be updated.
Q.15.What are the advantages of React Native?
A. Few significant advantages of React native are as following:
Conveniently uses the client as well as server side
Superbly cost effective and code reuse
Better code readability because of JSX use
Easy to integrate with other significant frameworks
Easy to write UI test cases because of React
Q.16.What are the features of React?
A. Major features of React are listed below:

  1. It uses the virtual DOM instead of the real DOM.
  2. It uses server-side rendering.
  3. It follows uni-directional data flow or data binding.
Q.17.Why can’t browsers read JSX?
A. Browsers can only read JavaScript objects but JSX in not a regular JavaScript object. Thus to enable a browser to read JSX, first, we need to transform JSX file into a JavaScript object using JSX transformers like Babel and then pass it to the browser.
Q.18.What is Props?
A. Props is the shorthand for Properties in React. They are read-only components which must be kept pure i.e. immutable. They are always passed down from the parent to the child components throughout the application. A child component can never send a prop back to the parent component. This help in maintaining the unidirectional data flow and are generally used to render the dynamically generated data.
Q.19.What is a state in React and how is it used?
A. States are the heart of React components. States are the source of data and must be kept as simple as possible. Basically, states are the objects which determine components rendering and behavior. They are mutable unlike the props and create dynamic and interactive components. They are accessed via this.state().
Q.20.What are the different phases of React component’s lifecycle?
A. There are three different phases of React component’s lifecycle:

  1. Initial Rendering Phase: This is the phase when the component is about to start its life journey and make its way to the DOM.
  2. Updating Phase: Once the component gets added to the DOM, it can potentially update and re-render only when a prop or state change occurs. That happens only in this phase.
  3. Unmounting Phase: This is the final phase of a component’s life cycle in which the component is destroyed and removed from the DOM.
Q.21.Explain the lifecycle methods of React components in detail.
A. Some of the most important lifecycle methods are:

  1. componentWillMount()  Executed just before rendering takes place both on the client as well as server-side.
  2. componentDidMount()  Executed on the client side only after the first render.
  3. componentWillReceiveProps() – Invoked as soon as the props are received from the parent class and before another render is called.
  4. shouldComponentUpdate()  Returns true or false value based on certain conditions. If you want your component to update, return true else return false. By default, it returns false.
  5. componentWillUpdate() – Called just before rendering takes place in the DOM.
  6. componentDidUpdate()  Called immediately after rendering takes place.
  7. componentWillUnmount() – Called after the component is unmounted from the DOM. It is used to clear up the memory spaces.
Q.22.What is an event in React?
A. In React, events are the triggered reactions to specific actions like mouse hover, mouse click, key press, etc. Handling these events are similar to handling events in DOM elements. But there are some syntactical differences like:

  1. Events are named using camel case instead of just using the lowercase.
  2. Events are passed as functions instead of strings.

The event argument contains a set of properties, which are specific to an event. Each event type contains its own properties and behavior which can be accessed via its event handler only.

Q.23.What are synthetic events in React?
A. Synthetic events are the objects which act as a cross-browser wrapper around the browser’s native event. They combine the behavior of different browsers into one API. This is done to make sure that the events show consistent properties across different browsers.
Q.24.What do you understand by refs in React?
A. Refs is the short hand for References in React. It is an attribute which helps to store a reference to a particular React element or component, which will be returned by the components render configuration function. It is used to return references to a particular element or component returned by render(). They come in handy when we need DOM measurements or to add methods to the components.
Q.25.List some of the cases when you should use Refs.
A. Following are the cases when refs should be used:

  • When you need to manage focus, select text or media playback
  • To trigger imperative animations
  • Integrate with third-party DOM libraries
Q.26.What can you do with HOC?
A. HOC can be used for many tasks like:

  • Code reuse, logic and bootstrap abstraction
  • Render High jacking
  • State abstraction and manipulation
  • Props manipulation
Q.27.What are Pure Components?
A. Pure components are the simplest and fastest components which can be written. They can replace any component which only has a render(). These components enhance the simplicity of the code and performance of the application.
Q.28.What is the significance of keys in React?
A. Keys are used for identifying unique Virtual DOM Elements with their corresponding data driving the UI. They help React to optimize the rendering by recycling all the existing elements in the DOM. These keys must be a unique number or string, using which React just reorders the elements instead of re-rendering them. This leads to increase in application’s performance.
Q.29.What were the major problems with MVC framework?
A. Following are some of the major problems with MVC framework:

  • DOM manipulation was very expensive
  • Applications were slow and inefficient
  • There was huge memory wastage
  • Because of circular dependencies, a complicated model was created around models and views
Q.30.What are the three principles that Redux follows?

  1. Single source of truth: The state of the entire application is stored in an object/ state tree within a single store. The single state tree makes it easier to keep track of changes over time and debug or inspect the application.
  2. State is read-only: The only way to change the state is to trigger an action. An action is a plain JS object describing the change. Just like state is the minimal representation of data, the action is the minimal representation of the change to that data.
  3. Changes are made with pure functions: In order to specify how the state tree is transformed by actions, you need pure functions. Pure functions are those whose return value depends solely on the values of their arguments.
Q.31.What do you understand by “Single source of truth”?
A. Redux uses ‘Store’ for storing the application’s entire state at one place. So all the component’s state are stored in the Store and they receive updates from the Store itself. The single state tree makes it easier to keep track of changes over time and debug or inspect the application.
Q.32.List down the components of Redux.
A. Redux is composed of the following components:

  1. Action – It’s an object that describes what happened.
  2. Reducer –  It is a place to determine how the state will change.
  3. Store – State/ Object tree of the entire application is saved in the Store.
  4. View – Simply displays the data provided by the Store.
Q.33.Explain the role of Reducer.
A. Reducers are pure functions which specify how the application’s state changes in response to an ACTION. Reducers work by taking in the previous state and action, and then it returns a new state. It determines what sort of update needs to be done based on the type of the action, and then returns new values. It returns the previous state as it is, if no work needs to be done.
Q.34.What is React Router?
A. React Router is a powerful routing library built on top of React, which helps in adding new screens and flows to the application. This keeps the URL in sync with data that’s being displayed on the web page. It maintains a standardized structure and behavior and is used for developing single page web applications. React Router has a simple API.
Q.35.Why is switch keyword used in React Router v4?
A. Although a <div> is used to encapsulate multiple routes inside the Router. The ‘switch’ keyword is used when you want to display only a single route to be rendered amongst the several defined routes. The <switch> tag when in use matches the typed URL with the defined routes in sequential order. When the first match is found, it renders the specified route. Thereby bypassing the remaining routes.