16 Essential React Native Interview Questions

1. The community for React Native is big. Due to the Open Source Framework's total community involvement, any issues can be handled by consulting other developers online.
2. Because no separate teams are required to support iOS and Android, React Native enables code to be developed once and utilized for all platforms. This makes managing and debugging complicated applications easier and significantly lowers costs.
3. Another benefit is live and instant reloading. When a file changes, live reloading reloads or refreshes the entire app. For instance, live reloading would restart the program and load it to the starting path if you were four links into your navigation and saved a change.
   Hot reloading keeps the application's state intact while simply refreshing the updated files. For instance, if you saved a change to some styling while four links into your navigation, the state would not change, but the new styles would appear on the page without requiring you to return to the page you are currently on because you would still be there.
4. Additionally, React Native supports other third-party plugins. React Native has third-party plugins that can be used if the built-in modules do not satisfy the business requirement, which could hasten the development process.
5. For any customer-facing applications that do not substantially rely on OS-specific features and integrations, such as AR and VR, or do not require elaborate design or animations to establish a competitive advantage, React Native is a suitable framework. React Native speeds up the development process and provides enough tools and modules to create a reliable application.
6. Another benefit is that creating a React Native mobile app is simpler when your online app is written in React.

Yes, default props are available in React Native, just as in React. For example, the component will use the default props value if the props value is not given.

import React, {Component} from 'react';

import {View, Text} from 'react-native';
class DefaultPropComponent extends Component {
   render() {
       return ( 
           
              
              {this.props.name} 
             
          
       )
   }
}
Demo.defaultProps = {
   name: 'John'
}

export default DefaultPropComponent;

Note: Commonly asked React Native interview question.

React 16.8 includes a new improvement called hooks. Without involving the class, they enable the use of the state, and other react functionalities. Utilizing hooks is primarily done to address side effects in the React functional components.

import React, { useState } from 'react';

function Example() {
  // Declare a new state variable, which we'll call "count"
  const [count, setCount] = useState(0);

  return (
    <:div>
      <:p>You clicked {count} times</p>
      <:button onClick={() => setCount(count + 1)}>
        Click me
      <:/button>
    <:/div>
  );
}

useState is a Hook in this case. To provide it with some more local state. Between re-renders, React will keep this state.

The current state value and a method that enables updating it are returned as a pair by useState. This function can be used elsewhere or in an event handler. It is comparable to this.

setState in a class differs from mergeState in that it doesn't combine the existing and new states.

The starting state is the only argument given to useState. The previous example is zero since our counter begins at zero. Notably, the state, in this case, does not have to be an object, unlike this.state. Only the initial render makes use of the initial state argument.

The fundamental element that enables text entry is called TextInput. It contains two properties: a onChangeText prop that will be called whenever the text changes and a onSubmitEditing prop that will be called after the content is submitted.

import React, { useState } from 'react';
import { Text, TextInput, View } from 'react-native';

const MoneyTranslator = () => {
 const [text, setText] = useState('');
 return (
   
      setText(text)}
       defaultValue={text}
     />
     
       {text.split(' ').map((word) => word && '💰').join(' ')}
     
   
 );
}

export default MoneyTranslator;

import React, {Component} from 'react';    
import { Text, View } from 'react-native';    
export default class App extends Component {    
 state = { 
myState: 'State of the Text Component'
              }
updateState = () => this.setState({myState: 'State is now updated'})
render() {
return (
    
 {this.state.myState}     
 
); } }

As a simple illustration of how State functions in React Native, this code is provided. The state controls the components. The state can store the variable data. Because it is mutable, a state may at any time modify the value, too.

With state information, the code builds a Text component. Every time we click on the Text component, the content is updated. Event onPress updates the state.

Note: Commonly asked React Native interview question.

The React Native Timer uses the same methods as the standard JavaScript timer and is an implementation of that timer.

Code typically executes synchronously, or one line at a time, with each line only starting to run once before it has finished. However, when running code asynchronously or according to conditions rather than in a set, the order is frequently much better.

We can run sections of code asynchronously for predetermined amounts of time using the React Native Timer.

So, as mentioned, React Native implements the browser timers, a crucial and essential component of any application. Let’s look at its main examples.

setTimeout, clearTimeout

setTimeout can be used when there are business requirements to run a particular piece of code after a certain amount of time has passed or after a delay; clearTimeout is simply used to stop the timer that has already been started.

setTimeout(() => {
yourFunction();
}, 3000);

setInterval, clearInterval

The method setInterval uses the second parameter to specify exact time intervals at which to execute a function or other pieces of code.

setInterval(() => {
console.log('Interval triggered');
}, 1000);

An interval-bound function or block of code runs until it is halted. The clearInterval() method can be used to end an interval.

setImmediate, clearImmediate

Calling the function or execution as soon as possible.

var immediateID = setImmediate(function);
// The below code displays the alert dialog immediately.
var immediateId = setImmediate(
    () => {    alert('Immediate Alert');
}

To reverse the immediate actions that setImmediate had set, use clearImmediate(). requestAnimationFrame, cancelAnimationFrame

It is how animations are typically done. updating an animation before the subsequent animation frame by calling a function.

var requestID = requestAnimationFrame(function);
// The following code performs the animation.
var requestId = requestAnimationFrame(
    () => { // animate something}
)

cancelAnimationFrame is used for canceling the function that was set by requestAnimationFrame().

One of the well-liked libraries for routing and navigation in a React Native application is React Navigation.

This library aids in the solution of data sharing and navigating between several screen issues.

import * as React from 'react';
import { NavigationContainer } from '@react-navigation/native';
import { createStackNavigator } from '@react-navigation/stack';

const Stack = createStackNavigator();

const MyStack = () => {
 return (
   
     
       
       
     
   
 );
};

The fact that each thread—both the Native and JS threads—is blazingly fast is why React Native experiences performance concerns.

The React Native app's performance is slowed down when components are sent from one thread to another more frequently than is necessary.

Another performance issue occurs when unnecessary processes run in an Android app's background, causing memory leakage.

Furthermore, navigational performance is crucial, just as an app's overall performance. It will be challenging for the user to access different app elements if the navigation performance isn't fluid. Users might not use your interface if moving between screens is difficult.

In general, it is good to keep the number of passes across the bridge to a minimum in React Native, as this is a key rule of thumb to follow to prevent any type of performance-related issues.

Other than this, when experiencing performance issues, I would consider the following steps:

• Employ scrollable lists
• Reduce the size of the image
• Reduce application size
• Reduce the number of dependencies.
• Utilize only high-performance components.
• Remove all unused renderings
• Use the React Native Navigation tool

Note: Commonly asked React Native interview question.

Higher-Order-Component is an advanced React Native technique to reuse the component logic. The function obtains a component and returns a new element. Following is a code example.

function HOC(Comp) {
     return class NewComp extends Component {
         render() {
            return 
         }
    }
}

React Native is a base derivative in and of itself, meaning that the components are different, but the syntax and workflow are the same. ReactJS is a base derivative of React DOM for the web platform.

ReactJS is a JavaScript toolkit that lets programmers build attractive and effective UI Layers. At the same time, React Native is an entire framework for building cross-platform apps, be it web, iOS, or Android.

While React Native uses native APIs to draw components on mobile devices, ReactJS uses virtual DOM to render browser code. Also, while React Native employs Javascript-based JSX for UI rendering, ReactJS apps render HTML in the user interface.

In addition, styling in ReactJS is done with CSS, but styling in React Native is done with a stylesheet.

Like in web design, CSS is used in ReactJS to provide animation. In React Native, the animation is induced across various React Native application components via an animated API.

Last but not least, Reactjs is the ideal choice if you need to create a high-performing, dynamic, and responsive UI for web interfaces, whereas React Native is the best choice if you need to give mobile apps a fully native experience.

The geolocation API expands the web standard for geolocation. Android uses the android.location.API for geolocation.

The new Location Services API is integrated into React Native using the following alternate libraries:

React-native-geolocation-service
React-native-location

The following code must be present in the AndroidManifest.xml file of the application to request location access:

<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/>

Note: Commonly asked React Native interview question.

A Button component from React Native shows platform-specific buttons. The example below demonstrates how to use React Native to generate a platform-specific default button.

Platform-specific buttons have different looks and feel depending on whether the application runs on iOS or Android, as the term implies. Title and onPress are the two primary props that the button component exposes.

The text on the button is shown using title properties. A callback called onPress props is triggered when a user presses a button. This is extremely comparable to a web browser's click event. The React Native Button component is not styleable.

import React from 'react';
import { View, Alert, Button, StyleSheet } from "react-native";

const BasicButton = (props) => {
    return ( <Button style={styles.button} onPress={() => Alert.alert("You pressed the button")} title="Button"/> );
};

const styles = StyleSheet.create({
    button: {
        padding: 10,
        color: '#0055B2'
    }
});

export default BasicButton;

When the user touches the button in the example above, a platform-specific alert will be displayed. The React Native framework's Alert component displays the platform-specific modal.

As I previously stated, the Button component of React Native cannot be styled. However, we can try this by altering a button's text color or padding using style properties, but this won't change the button's appearance.

This code is used to access a native API. The value of robotscopePosition will always be an unfulfilled promise. Hence this code will always produce an error.

It's critical to remember that the asynchronous bridge between JavaScript and native code is necessary. We can either pass in a callback (which is not done in this case) or return a Promise to get results from this side. In this instance, we must set the position inside a then() function after the robotPosition() call.

React Native's StyleSheet module enables us to construct immutable stylesheet references. The module will freeze any common style objects we feed into the create() method and give each one an ID.

This has two advantages:

• it allows us to send the object through the asynchronous bridge only once,
• and it prevents us from building a new style object for every render pass, which could result in a decrease in render performance (since these style objects map directly to native styles, they need to be passed across).

The main disadvantage of this approach is that some infrastructure is required to decide which styles to employ when recomputing styles based on external criteria (such as screen rotation or even a user-selected viewing mode). Objects might be recomputed on-the-fly regularly based on arbitrary criteria if they were passed in "raw."

A React Native component called WebView is used to load web pages or other web resources. It comes from the react-native library's core.

React Native's WebView is replaced with the built-in core housed in the react-native review library. To put it another way, WebView acts as a bridge between React Native and online platforms, giving users various ways to connect to web-based applications.

Additionally, WebView can load an application into a web page and manage navigation.

It also doesn't require installation or configuration.

Note: Commonly asked React Native interview question.

A native React Native module called the InteractionManager is in charge of delaying the execution of a function until an interaction is complete. We must make the InteractionManager call to manage this deferral.

Due to React Native's two threads, the InteractionManager is crucial. The first is the JavaScript UI thread, which manages to update the screen's drawing, and the second is utilized for any operations that aren't on the UI thread.

React Native only has one thread for updating the user interface, which can lead to overload and frame drops, especially in animations for navigation screens. To ensure that the function is executed after these animations, developers employ the InteractionManager. As a result, we do not drop frames on the UI thread.