React Native Developer Interview Questions and Answers for 2024
Do you need to hire React Native developers and need React Native developer interview questions?
React Native is very popular for cross-platform mobile development. The Stack Overflow Developer Survey 2023 shows that the React Native framework is the 12th most popular software development framework.
At DevTeam.Space, we have extensive React Native application development expertise. Naturally, we can provide you with excellent React Native interview questions. You are on just the right page! You first need to understand what it takes a hire a React Native developer though.
Publish an effective and persuasive React Native job advertisement
Since many organizations prefer cross-platform mobile apps, they undertake React Native app development. You can see why React Native developers are in great demand. Given this backdrop, you certainly need to post an eye-catching job ad.
Do include the following in the job ad:
Company descriptions
Surely, you will provide factual descriptions of your organization. You need to do more than that to attract top React Native developers though. Describe why your organization is the right place for the right talent.
Talk about your organizational culture and how it helped in achieving high growth. Elaborate on the professional development opportunities you offer. Describe the work environment, compensation policies, and benefits. Emphasis on the growth opportunities available to developers.
Job descriptions for React Native app developers
React Native developers design and develop React Native apps. They might also maintain and enhance React Native apps. You will surely write about these in the job description, however, you need to write more to attract top talents. Mention how the work of React Native developers will help your organization grow. Tie your organizational growth to the overall growth opportunities for developers, which will appeal to quality React Native developers.
React Native developer roles and responsibilities
React Native developers know that they need to code React Native mobile apps. They also know that they will debug React Native apps and test them. Therefore, you need to highlight the roles and responsibilities that will make them interested in your organization.
Stress upon tasks like architecting the app, deciding on the UI design parameters, communicating with business stakeholders, etc. Include the following when you write the roles and responsibilities of React Native developers:
- Developers will need to provide important inputs to the architect or take an active part in architectural decision-making.
- React Native developers will participate in making key decisions regarding the UI design of the app.
- Provide key inputs to the business stakeholders to make the React Native app development project successful.
- Analyze requirements and build technical solutions to create a React Native app.
- Code, test, and deploy the app.
- Maintain and enhance React native applications.
- Provide effective status reports to the relevant stakeholders.
- Collaborate effectively with the larger team.
React Native developer skills
You would ideally want a React Native developer to have a bachelor’s degree in computer science, information technology, or a related field. Mention this requirement, furthermore, include the following skill requirements:
- The developer needs comprehensive skills and experience in React Native.
- React Native programmers should understand React JS sufficiently. They should know the React Native components, furthermore, programmers need good experience in developer tools like React Native CLI.
- A React Native developer should know JavaScript, HTML, and CSS well.
- You should look for developers who understand TypeScript.
- React Native developers need very good knowledge of the key operating systems like Android, iOS, and Windows.
- They should understand important programming paradigms like object-oriented programming (OOP) and functional programming.
- Developers need to understand important architectural patterns like MVC (Model View Controller).
- React Native coders should know about RESTful API development.
- You would want developers to know open-source frameworks and tools relevant to your project.
- React Native developers should know important SQL databases like MySQL and PostgreSQL. They also need to know about NoSQL databases like MongoDB.
- Programmers need knowledge of testing frameworks like Jest and Mocha.
- You need developers with a good understanding of testing and DevOps.
- React Native developers require performance-tuning experience.
- They need competencies like communication skills, teamwork, passion for excellence, etc.
React Native interview questions and answers for hiring junior developers
When you need to hire junior React Native developers, you can use the following interview questions and answers:
1. How will you align elements of a UI design vertically or horizontally in React Native?
We can use the React Native Flexbox to align UI (user interface) design elements vertically or horizontally in React Native. Flexbox is a useful layout model available in React Native.
You can find several properties of this layout model, and the “flexDirection” property is used for the vertical and horizontal alignment of UI design elements. While using this property, you need to use the values “column” and “row”.
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2. Explain how you will make React Native components reusable.
We can use the React Native properties to make components reusable. Developers often call properties “props”. Programs can only read the React Native properties since they are immutable.
Taking advantage of this immutability, we can pass data from a React Native parent component to a child component. Depending on the use of a component, we provide different data to it via properties. The immutability of React Native “props” allows us to maintain a data flow in one direction only.
3. I have a React Native mobile app development project where the app will perform several operations requiring high-intensity computation. I am already looking at performance optimization measures in the areas of database and infrastructure. Therefore, suggest only React Native-specific optimization measures for my project.
You can use React Native hooks named “useMemo” and “useCallback”, a few React Native-specific optimization measures to develop mobile apps that can perform computationally-intensive operations efficiently. These two React Native hooks can take some load off the React Native functional components.
The “useMemo” hook remembers values. The app will not need to perform computation-heavy calculations again and again if you use this hook. Use this hook when there are no changes to the dependencies.
The “useCallback” hook remembers functions. The app will not need to recreate the functions during every render if you use this hook. You can then avoid unnecessary re-renders of functional components.
4. In my proposed React Native app, I will have a button that users will press and hold. The app should provide feedback to users for this action. I am deciding on whether the app should highlight the background of the button or the opacity of the button should be reduced. Explain how I can achieve either of these outcomes.
You can do the following:
- Pass a function to the “onLongPress” property to either of the following “Touchable” components of React Native: “TouchableHighlight”, and “TouchableOpacity”.
- If you want to highlight the background of the button, then use the “TouchableHighlight” React Native component.
- Use the “TouchableOpacity” component if you want to reduce the opacity of the button.
- Keep in mind that these components don’t come with any default styling. Therefore, you need to do write a bit of additional React Native code so that the interaction looks good to users.
5. Explain a quick way to create custom maps while developing a React Native app.
An easy way to create a custom map in React Native is to use an open-source native component named MapLibre. React Native has a thriving developers’ community. These developers create many open-source tools for React Native including native components.
Developers can access the MapLibre SDK on GitHub via the React Native directory, which has many such React Native libraries. They can use it for both iOS and Android.
6. You are enhancing a React Native app, and you are currently 5 links deep into the navigation. Having modified the style of a user input field, you want to see the changes immediately on the same page. Explain how you can achieve this.
I will use “Hot reloading”, one of the key features of React Native to accomplish this. The “hot loading” process only updates and refreshes the file changed by a developer. This process makes no changes to the state of the React Native app.
I will not need to navigate again from the beginning since the “hot reloading” process will not change the state. I will get to see the changes to the style on the same page where I am.
7. Which React Native debugging tool helps you to debug React components too? Also, mention constraints if there are any.
React’s Developer Tools helps us to debug React Native apps including React components.
The only constraint we have concerning debugging React Native apps using this tool is that we need to use the desktop version of React’s Developer Tools. It’s not a major constraint. We can easily install this tool using npm or yarn.
React Native developer Interview questions and answers for hiring mid-level developers
Use the following questions when taking React Native interviews for hiring mid-level programmers:
1. There’s an Instagram-like Android app developed using React Native which crashes often. What will you investigate first? If you detect that issue you anticipated, then how will you resolve it?
Instagram-like Android apps created using React Native sometimes crash since the list of images doesn’t get recycled when one scrolls. The garbage collection process doesn’t work. There’s no manual clean-up either.
The app crashes due to an out-of-memory (OOM) issue, which is common with this type of React Native app. I will first investigate this possibility.
For this investigation, I will analyze the heap memory usage of the app using Android Studio. I will scroll through the list of images. If I notice the heap usage rapidly growing and not reducing at all, then it’s an OOM issue.
Often, the root cause is the use of the “ListView” component. We should use the “FlatList” component instead of “ListView”. I should also reduce the resolution of the images.
2. How will you easily achieve responsiveness in a React Native app?
3 modules from the React Native library can help considerably to achieve responsiveness. These are as follows:
- Dimensions;
- Platform;
- PixelRatio.
Developers should import these 3 modules using the following command: Import from ‘react-native’.
Using the “Dimensions” module, React Native developers can dynamically access the screen dimensions of a device. This module valuable information like the width and height of the screen.
Developers can use the “Platform” module to find out the operating system of the device. They can then adjust the behavior of the app to the platform, e.g., native iOS.
PixelRatio is one of the React Native core components. This component helps developers to convert the pixel values from the device-independent pixel to the physical pixel.
3. Explain how you will synchronize React Native animations with the refresh cycle of the browser.
We can do the following:
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- We use “requestAnimationFrame”, a browser and React Native API.
- When we invoke “requestAnimationFrame”, it executes the animation callback immediately before the browser can redraw the screen.
- This aligns the flow of the animation with the display refresh rate of the device.
- The above-mentioned alignment reduces the risk the animation stuttering.
This way, the “requestAnimationFrame” optimizes the animation to give a seamless experience to users.
4. Show an example of using the React Native text component.
The following code snippet shows an example of using the text component in React Native:
“
Import React from ‘react’;
Import { Text, View } from ‘react-native’;
Import Icon from ‘react-native-vector-icons/AntDesign’;
const App = () => { return ( <View> <Text style={{fontFamily: ‘CustomFont’, fontSize: 20 }}>Custom Font Example </Text> <Icon name=”printer” size={40} color=”#900” /> </View> ); };
export default App;
“
5. How will you make the execution of a React Native function wait until the completion of an interaction?
We can use a native module named “InteractionManager” for this purpose. It can delay the execution of a React Native function until an interaction has ended. The following is the syntax for using this module:
“
InteractionManager.runAfterInteractions(() => {…….}}
“
To use “InteractionManager” for an interaction of particular interest to us, we can register that interaction.
6. How does React Native minimize the updates to the actual DOM (Document Object Model)?
React Native uses a Virtual DOM similar to React. When React Native detects changes to the properties or state of a component, it creates a new Virtual DOM tree.
Subsequently, React Native compares the new Virtual DOM tree with the earlier one. This process is known as “reconciliation”.
React Native then communicates with the native iOS or Android platform’s UI elements. Via this route, React Native gets the actual DOM updated with only the changes required.
7. React Native is a cross-platform mobile framework and not a native application development technology like Swift, Kotlin, or Java. How will you access native platform capabilities like accessing device sensors?
Although React Native is a cross-platform mobile development framework and not a native application development technology, it still offers native modules. These JavaScript modules help the JavaScript code underlying React Native to utilize platform-specific APIs.
For example, a React Native app can access native APIs via these native modules. These native modules facilitate tasks like communicating with device hardware, accessing device sensors, etc. Several such modules to access native code exist for multiple platforms like Android and iOS.
Senior React Native app developer interview questions and answers
Hiring React Native experts? Use the following React Native interview questions to evaluate their skills:
1. In a React Native Android app, the image is much bigger than the view. How will you resize the image?
I will use the “resizeMethod” mechanism for the image component of React Native. Within that, I should use the “resize” option. This changes the size of an encoded image in the memory before decoding it. It’s the right option when the image is bigger than the view.
2. Find the error in the below code.
Code snippet:
class Runnerpos {
setRunnerPosition(pos) {
if (pos === null || typeof pos === ‘unknown’) {
throw new Error(‘The position is not defined’);
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}
this.pos = pos;
}
constructor() {
const RunPosition = NativeModules.MyRunModule.RunnerPosition();
this.setRunnerPosition(RunPosition);
}
}
Answer:
This code will always result in an unresolved “Promise” in the value of “RunPosition”. The React Native bridge connects native code and JavaScript, and it’s asynchronous. You have 2 options to receive a result.
First, you need to pass a callback. You haven’t done that in this code snippet.
Second, you can return a “Promise”. In that case, you need to add a “then()” call within the “RunnerPosition()” call. You would need to set the position inside that call.
You will receive an error since none of the above conditions are satisfied in this code snippet.
3. I want to use “Animation.spring” in my planned React Native app. I want a native performance for this animation. Explain how I can accomplish this.
This animation type can be computed ahead of time. Therefore, it can be serialized. React Native can send this animation via the asynchronous bridge before it’s executed. The runtime will then defer the actual drawing of Animation.spring to the native side. The React Native runtime will not need to send positional values for the rendering of every frame. Therefore, your app will process this animation just like a native app does.
4. Provide a suggestion to improve React Native application startup performance and reduce memory consumption.
We can improve React Native app startup performance and reduce memory consumption by using the Hermes JavaScript engine. The React Native project team is working towards enabling developers to use it seamlessly.
The Hermes JavaScript engine uses an architectural concept called “Bridgeless architecture”. This architectural pattern and the Hermes engine reduce the communication overhead between the native code and JavaScript code.
This architecture reduces the requirements for data serialization and deserialization across the React Native bridge. The app startup performance improves as a result, with a reduction in memory consumption.
5. In my proposed React Native app, I need to use long lists of data. Suggest how I can achieve an optimal rendering performance.
We can use the React Native component named “VirtualizedList” to optimize the rendering of long lists of data elements. This component doesn’t render all items in the list at the same time.
It picks only the data items that can be seen within the viewport. “VirtualizedList” renders these elements. Subsequently, the app user scrolls. “VirtualizedList” then recycles data and renders the next set of data elements. Your app will then achieve the desired rendering performance.
6. I want to integrate 3rd party web services into my proposed React Native app. Suggest how I can do this. Also, pinpoint any constraints with your suggested approach.
You can use the React Native component named “WebView” to integrate 3rd party web services into your React Native app. It allows you to embed web content as a different view within your app. Therefore, you can embed HTML, JavaScript, etc. Not just 3rd party web services but you can also render 3rd party webpages and interactive web-based components using “WebView”.
Before you decide to use the “WebView” component, take a close look at the external web service or webpage. Make sure that the security, responsiveness, and loading time of your app don’t take a hit due to them.
Planning to hire React Native developers?
Our comprehensive set of React Native interview questions and answers should help you to interview developers. However, interviewing React Native developers can take time, especially if you interview freelancers. Given that your React Native app development project is important to your organization, can you afford to spend that time? Remember that verifying the relevant experience of freelancers can be hard.
Your best bet is to hire full-time, skilled, experienced, and motivated developers from a trusted partner like DevTeam.Space. You can then take advantage of our comprehensive vetting process, and you don’t need to spend much time interviewing.
Just fill up the DevTeam.Space product specifications form. A dedicated account manager will soon help you.
