Senior React.js interview questions and answers for 2023
The way you interview senior React developers is different than how you would for junior and mid-level roles. This is because the roles, responsibilities, and skill requirements are very different between each level.
For senior React developers, specifically, there’s a large emphasis placed on years of experience. Experience is the one signal that will determine whether a developer has seen enough in the wild to come up with meaningful solutions based on, well, their experiences!
Mind blown? Don’t worry, it gets better.
Of course, we expect senior React developers to know the fundamentals of their library of choice, and they should also be able to solve a variety of popular advanced cases that make user experiences feel delightful and truly high-quality.
But more importantly, they need to communicate well with their team and demonstrate real-world experience through the stories they tell. It’s very hard to fake the experience.
If you’re looking to properly interview and validate your senior React developers on a technical and non-technical level, we got you covered. Below are some technical and non-technical questions you can use in your next interview.
Technical Questions for senior react developers
Is there a way to cancel a request inside a useEffect?
The following code doesn't preserve the component state when isFavorite changes, how can you prevent/fix this?
When a component is rendered in a React app, its state is preserved as long as it remains in the UI tree. This can cause issues if the component is unmounted and then remounted at a different position in the tree, as its state will be lost.
To prevent this, you can render the component within the same parent div to ensure that its state is preserved even if it is moved around in the UI tree. This way, the component can be safely unmounted and remounted without losing its state.
What's the main difference between useMemo and useCallback and when would you want to use and avoid them?
The useMemo hook is used to memoize the value of a function, optimizing expensive calculations, while useCallback is used to memoize the function itself, optimizing the performance of child components.
Use useMemo when you want to memoize a value and avoid recomputation, and use useCallback when you want to memoize a function and prevent unnecessary re-renders of child components.
Use it: useMemo is used when you want to optimize the performance of expensive calculations or complex operations that are not related to rendering. It allows you to avoid unnecessary recalculations when the inputs haven’t changed.
Don't use it: useMemo should not be used for side effects or as a replacement for useEffect. If you need to perform an action that has side effects (such as modifying the DOM or fetching data), you should use useEffect instead.
Use it: useCallback is used when you want to optimize the performance of child components that rely on callbacks. By memoizing the callback function, you can ensure that child components only re-render when the dependencies of the callback change, rather than on every render.
Don't use it: useCallback should not be used excessively or prematurely. It’s best to use it when you notice actual performance issues related to unnecessary re-renders of child components.
React Problem/Scenario Questions
These questions are quasi-technical questions that focus on general problem-solving within the context of ReactJS.
How do you ensure that React components are shared effectively across your development team and well documented so that everyone has access to the latest version of each component?
Of course, there are no wrong answers here but a good alternative is to use Storybook. With Storybook you are able to build UI components and pages in isolation. Some cool benefits of Storybook:
- Tests: Visual tests, interaction tests, accessibility tests, coverage tests, and snapshot tests.
- Documentation: generate UI docs automatically
- Reusability: reuse components across pages and apps
- History: track components' history and versions
If you want to install it in your application, please follow these steps.
Non-technical questions for senior React developers
Could you tell us about a project where you had to integrate React.js with other technologies/platforms?
It's common to combine platforms and technologies with React.js. This question is used to assess a candidate's familiarity with integrating React.js into different contexts as well as their versatility when it comes to using different tools and technologies.
A good answer to this question is a story where they demonstrate their overcoming the challenges associated with integrating React. They’ll present details that would be hard to fabricate otherwise.
There is no wrong answer to this question, only vague answers that indicate that the developer chose not to be honest about the fact that they did not integrate React. The signal to consider is that in cases where they might be under pressure, they might provide misinformation which can be problematic down the road.
How do you ensure that your code is maintainable and easy for others to understand and work with?
Maintainable code is code that is easy to read, understand, and modify.
Keep in mind that other developers will work with your code when creating a React.js application, therefore you should make sure it is as simple as possible for them to do so.
It's important to describe the steps you take to ensure that your code is maintainable. Be sure to mention descriptive variable naming, breaking code down into smaller pieces, modularization, separation of concerns, etc.
Great teams think about these types of things in advance. They create code standards and guidelines that ensure consistency across the codebase no matter who is writing.
Senior ReactJS developers who come from teams like these will know and understand the value of standardization and will most likely seek to continue working on teams that share their values.
3 min read
The choice of a front-end framework is a pivotal decision that can significantly impact the success of your web development project. In the ever-evolving landscape of web development, NextJS and ReactJS have emerged as two prominent options garnering widespread adoption.
This article delves deep into the intricacies of NextJS and ReactJS, shedding light on their unique features, benefits, and key considerations.
By gaining a comprehensive understanding of these frameworks, you will be equipped to make an informed decision that aligns with your project's requirements and sets you up for success.
What is React
This approach allows developers to build reusable and modular components, making code organization and maintenance a breeze. Additionally, ReactJS utilizes a virtual DOM (Document Object Model) to efficiently update and render UI elements, resulting in better performance and a smoother user experience.
React’s key features include:
- Component reusability: React promotes the creation of modular and reusable UI components, making it easier to build complex interfaces.
- Virtual DOM: React's virtual DOM efficiently updates only the necessary parts of the user interface, improving performance.
- Unidirectional data flow: React follows a one-way data flow, making it easier to track changes and maintain application state.
- Rich ecosystem: React has a vast ecosystem of libraries, tools, and community support, making it suitable for a wide range of use cases.
The ReactJS ecosystem is vibrant and constantly evolving. It offers a wide range of third-party libraries, tools, and community support. Developers can find solutions for various requirements, from state management (using hooks like useState and useContext) to global state management (with Redux).
The availability of numerous resources, forums, and tutorials ensures that learning ReactJS is both accessible and rewarding.
What is NextJS
Next.js, built on top of React, is a framework specifically designed for server-side rendering (SSR) and static site generation (SSG) in React applications.
Some key features and benefits of Next.js are:
- Server-side rendering (SSR): Next.js allows rendering React components on the server before sending them to the client, resulting in faster initial page loads and improved SEO.
- Static site generation (SSG): Next.js supports pre-rendering of entire pages at build time, enabling the generation of static HTML files for improved performance and better caching.
- File-based routing: Next.js provides a simple and intuitive file-based routing system, eliminating the need for complex routing configurations.
- API routes: Next.js allows the creation of serverless functions called API routes, enabling the development of backend functionality within the framework itself.
These additions simplify the development process and reduce the need for additional libraries or configurations.
NextJS shares many key features with React, including component-based development and the virtual DOM, and combines the power of React with server-side rendering capabilities, allowing developers to pre-render pages on the server and deliver HTML to the client. This approach improves initial page load times, enhances SEO (Search Engine Optimization), and provides a better user experience.
Getting Started with React
To start using React, you need to set up a development environment. Here are the basic steps to get started:
- Installation and setup: Install Node.js and npm (Node Package Manager) to manage dependencies. Then, create a new React project using tools like Create React App or manually configure the project structure.
Getting Started with Next.js
Next.JS, being a framework built on ReactJS, requires a similar development environment setup. You will need Node.js and a package manager. Fortunately, NextJS provides a streamlined setup process with its built-in create-next-app command, allowing you to quickly initialize a Next.JS project with minimal configuration
To begin working with Next.js, follow these steps:
- Installation and setup: Install Next.js using npm or yarn. Create a new Next.js project using the provided command-line interface (CLI) tool or manually set up the project structure.
- Creating a basic Next.js project: Create a pages directory where each file represents a unique route. Define the structure and content of the page using JSX syntax. Next.js automatically handles the routing for these pages.
- Understanding server-side rendering (SSR): With Next.js, components can be rendered on the server and sent to the client as HTML, providing a faster initial page load. Understand how Next.js handles SSR and the benefits it offers.
Both React.JS and Next.JS rely on various tools and dependencies to streamline the development process. Some commonly used tools include code editors like Visual Studio Code, version control systems like Git, and development servers like webpack-dev-server.
Additionally, libraries like React Router, CSS-in-JS libraries for styling, and testing frameworks can be utilized to enhance the development workflow.
React's popularity has led to the growth of a vibrant ecosystem consisting of libraries, tools, and community support. Here are some essential components of the React ecosystem:
- React Router: React Router is a popular library that provides client-side routing capabilities, allowing you to create navigation within a React application.
- State management with Redux or MobX: React itself offers basic state management, but for complex applications, libraries like Redux or MobX are commonly used to manage application state more efficiently.
- UI component libraries: Several UI component libraries, such as Material-UI and Ant Design, offer pre-built UI components and styling options to streamline the development process.
These components enhance the development experience and provide ready-to-use solutions for common challenges in building React applications.
Next.js has its own ecosystem, offering additional features and tools to augment the development process. Some notable aspects of the Next.js ecosystem include:
- Server-side rendering (SSR) benefits: Next.js brings server-side rendering capabilities to React, allowing for faster page loads and improved search engine optimization (SEO).
- File-based routing: Next.js simplifies routing by mapping files and directories to URLs, reducing the need for complex routing configurations.
- API routes for serverless functions: Next.js provides a built-in API routing system, allowing you to create serverless functions that can serve as backend endpoints.
These features make Next.js an attractive choice for projects that require server-side rendering and seamless API development.
Building reusable components is a fundamental aspect of both React.JS and NextJS. React.JS promotes a component-based architecture, where you break down your user interface into modular components that encapsulate their own logic and can be reused across your application. This modular approach simplifies maintenance, promotes code reusability, and improves collaboration between team members.
Similarly, Next.JS encourages the use of components to create reusable UI elements. However, Next.JS takes it a step further by providing built-in features like Layouts and Partials. Layouts allow you to create consistent structures for your pages, while Partials enable you to reuse smaller components within your layout.
When creating components in React.JS and Next.JS, it's important to follow best practices. This includes writing clean and concise
When it comes to performance, both React and Next.js have their strengths and considerations. Here's a comparison of their performance aspects:
- Performance considerations in React: React's virtual DOM diffing algorithm optimizes rendering, minimizing costly updates to the actual DOM. However, React primarily relies on client-side rendering (CSR), which can result in slower initial page loads and potential SEO challenges.
- Benefits of server-side rendering (SSR) in Next.js: Next.js addresses React's limitations by enabling server-side rendering, resulting in faster initial page loads and better SEO. By rendering components on the server, Next.js provides a fully rendered HTML page, improving performance and user experience. Understanding the trade-offs and implications of performance in React and Next.js can guide your decision-making process based on your project's specific requirements.
SEO and Next.js
Search engine optimization (SEO) is a critical aspect of modern web applications. Let's explore how Next.js addresses SEO challenges compared to React:
- Importance of SEO for web applications: SEO helps improve the visibility of a website on search engine result pages, driving organic traffic and increasing user engagement.
- SEO benefits of server-side rendering (SSR) in Next.js: Next.js' server-side rendering capabilities generate fully rendered HTML pages on the server, ensuring faster initial page loads and better search engine indexing. By leveraging Next.js' SSR capabilities, you can enhance your application's SEO performance and achieve better visibility in search engine rankings.
Deployment and Hosting
Deploying and hosting React and Next.js applications involve different considerations. Here are some deployment options and hosting platforms for both frameworks:
- Deployment options for React applications: React applications can be deployed to various hosting platforms, including cloud providers like AWS, Google Cloud, or Azure, as well as static site hosting services like Netlify or Vercel.
- Deployment options for Next.js applications: Next.js applications can also be deployed to cloud providers or static site hosting platforms. Additionally, Next.js offers features like serverless deployment to serverless computing platforms like AWS Lambda or Vercel's serverless functions.
Choose a deployment option and hosting platform that aligns with your project's scalability, performance, and cost requirements.
When to Choose React
While Next.js builds upon React, there are scenarios where using React alone might be more appropriate:
- Scenarios where React is a better choice: If your project has minimal server-side rendering (SSR) requirements and focuses on building client-side rendered applications or leveraging React Native for mobile app development, using React alone can be a suitable option.
- Projects with a different backend technology: If your project involves integrating with a custom server or a backend technology other than Node.js, using React without Next.js may offer more flexibility. Understanding these scenarios will help you determine if React is the ideal choice for your specific project requirements.
When to Choose Next.js
Next.js excels in scenarios that demand server-side rendering, improved SEO, and a simplified development experience for server-rendered applications. Here are some instances where Next.js shines:
- Scenarios where Next.js is a better choice: If your project requires server-side rendering (SSR) to enhance performance and SEO, or if you want a streamlined development experience with file-based routing and built-in API routes, Next.js is a powerful framework to consider.
- Projects with a need for enhanced SEO: Next.js' server-side rendering capabilities provide fully rendered HTML pages, ensuring better search engine indexing and improved SEO performance.
Next.js empowers developers to build performant, SEO-friendly applications with ease, making it a compelling choice for certain project requirements.
Should Your Hire A React or Next.js Developer?
Hiring React and Next.js developers can be a crucial step in ensuring the success of your projects. Consider the following technical aspects when hiring developers proficient in React and Next.js:
- Proficiency in React ecosystem: Look for candidates who have a solid understanding of the React ecosystem, including popular libraries and tools such as Redux, React Router, and styled-components. They should be familiar with best practices for state management, routing, and styling in React applications.
- Understanding of component-based architecture: React follows a component-based architecture, so candidates should have experience in building reusable and modular components. They should understand concepts like props, state, lifecycle methods, and hooks. Assess their ability to structure and organize components effectively.
- Experience with Next.js features: If you specifically require Next.js expertise, evaluate candidates' knowledge of Next.js specific features such as server-side rendering (SSR), static site generation (SSG), and API routes. Assess their ability to leverage Next.js to optimize performance, handle data fetching, and build server-rendered applications.
- Testing skills: React and Next.js applications can benefit from comprehensive testing. Look for candidates who have experience with testing frameworks and libraries like Jest, Enzyme, or React Testing Library. Assess their ability to write unit tests, integration tests, and end-to-end tests for React and Next.js components.
- Performance optimization: React and Next.js developers should be knowledgeable about performance optimization techniques. Evaluate candidates' understanding of code splitting, lazy loading, memoization, and other performance optimization strategies in React applications. Assess their ability to identify and resolve performance bottlenecks.
- Version control and collaboration tools: Proficiency in version control systems like Git and collaboration platforms like GitHub or GitLab is crucial for team collaboration. Ensure candidates have experience using Git for code versioning, branching, merging, and collaborating with other developers using pull requests.
- Familiarity with front-end build tools: Candidates should be familiar with front-end build tools like Webpack, Babel, and npm/yarn. Assess their ability to configure and customize build processes, handle dependencies, and optimize the bundling and minification of assets.
- Knowledge of responsive and mobile-first design: React and Next.js developers should understand responsive design principles and be able to build applications that work well across different devices and screen sizes. Assess their knowledge of CSS media queries, flexbox, and CSS Grid for responsive layouts.
- Problem-solving and debugging skills: Assess candidates' problem-solving and debugging abilities by asking them about challenging scenarios they encountered while working with React and Next.js. Evaluate their logical thinking, troubleshooting strategies, and familiarity with debugging tools like browser developer tools.
By considering these technical aspects during the hiring process, you can ensure that the React and Next.js developers you hire have the necessary skills and expertise to contribute effectively to your projects.
Choosing the right framework between Next.js and React depends on various factors. React offers a powerful library for building user interfaces, while Next.js extends React with features like server-side rendering (SSR) and simplified routing.
By understanding the features, benefits, and use cases of both frameworks, you can make an informed decision that aligns with your project requirements. Consider the performance implications, SEO considerations, and deployment options to determine whether React or Next.js is the best fit for your specific use cases.
If you’re considering hiring a senior React developer that knows Next.js and hoping to save a ton of time screening and interviewing, consider working with a tech partner like Trio to hire faster and smarter.
8 min read
What is Svelte?
Key features and benefits of Svelte:
Reactive Programming Model: Svelte embraces a reactive programming model where changes to the state automatically propagate throughout the application. This approach simplifies data handling and ensures that the UI stays in sync with the underlying data.
Component-based Architecture: Svelte encourages a component-based development approach, allowing developers to build reusable and modular components. This promotes code organization and enhances maintainability.
Performance advantages of Svelte:
Lightweight and Fast Runtime: Since Svelte compiles the code, it eliminates the need for a runtime library. This leads to a smaller bundle size, resulting in faster initial load times and improved runtime performance.
No Virtual DOM Overhead: Unlike React, which utilizes a virtual DOM, Svelte directly manipulates the DOM based on the changes in the state. This approach eliminates the virtual DOM reconciliation process, making Svelte even more performant.
Bundle Size Optimization: Svelte's compiler analyzes the code and optimizes the resulting bundle size. It achieves this by removing unused code and performing various other optimizations, resulting in a smaller overall bundle.
What is React?
React, developed by Facebook, has become a go-to choice for many developers due to its extensive ecosystem and robust community support. It offers a declarative and component-based approach to building user interfaces. React's popularity is largely attributed to its efficient updates through the virtual DOM.
Key features and benefits of React:
Virtual DOM and Efficient Updates: React utilizes a virtual DOM to efficiently update only the necessary parts of the user interface. By comparing the previous and current states, React intelligently updates the DOM, reducing unnecessary re-rendering and improving performance.
Large and Active Community: React boasts a massive and highly active community of developers. This active community ensures continuous development, extensive support, and a wealth of open-source projects and libraries.
Rich Ecosystem and Third-Party Libraries: React's ecosystem offers a wide range of third-party libraries and tools that facilitate rapid development and enhance functionality. From UI component libraries to state management solutions, React's ecosystem provides solutions for various needs.
Performance considerations with React:
Virtual DOM Reconciliation Process: While the virtual DOM enables efficient updates, the reconciliation (syncing) process between the virtual DOM and the actual DOM can introduce performance overhead. React minimizes this overhead by using smart diffing algorithms, but it's important to be mindful of potential performance bottlenecks.
Trade-offs between Performance and Flexibility: React's flexibility allows developers to create complex and dynamic user interfaces. However, as the complexity increases, performance can be impacted. Finding the right balance between flexibility and performance optimization is crucial.
Handling Complex Applications: React is well-suited for large-scale applications. However, developers need to carefully manage the state and component hierarchy to ensure optimal performance. Implementing efficient data flow and organizing components effectively is essential for complex React applications.
Svelte vs React: At-a-glance
Moderate to high
Web, mobile, desktop
Rapid prototyping, code reusability
Extensive ecosystem, community support
Front-end development approach
Reactive programming model
Virtual DOM and efficient updates
Direct manipulation of DOM
Lightweight and optimized
Lightweight runtime, fast
Efficient updates, performance optimizations required
Dynamic UI binding
Virtual DOM diffing
Two-way binding support
One-way binding (props)
Stores and reactive assignments
Local state, Redux, other librarie
Ideal use cases
Prototyping, interactive web apps
Large-scale apps, SSR, PWAs, native mobile apps
Facebook, Instagram, Netflix, Airbnb
Growing community, resources
Established community, vast resources
React Developer Tools, extensive tooling
Time to hire a senior developer
Detailed Comparison: React vs Svelte
Project Setup: Svelte vs. React
Setting up a project with Svelte:
To begin a Svelte project, you first need to install the Svelte compiler and setup a project structure. Once installed, you can start building components in Svelte using the Single-File Component (SFC) approach. Svelte provides a straightforward and intuitive syntax to define components, making it easy to get started.
Styling and CSS in Svelte:
Svelte offers various approaches for styling components. You can either use inline styles directly within the component or leverage CSS files and import them into the component. Svelte's approach to styling is flexible, allowing developers to choose the best method based on their preferences and project requirements.
Setting up a project with React:
Styling and CSS in React:
React doesn't enforce any specific styling methodology, leaving developers with the freedom to choose from various approaches. You can use inline styles, CSS modules, or even CSS-in-JS libraries like Styled Components or Emotion to style React components. This flexibility allows developers to adopt the styling approach that best suits their preferences and project requirements.
Learning Curve and Developer Productivity: Svelte vs React
Learning curve of Svelte:
Learning curve of React:
Comparing developer productivity:
Svelte offers rapid prototyping capabilities, thanks to its concise syntax and reactive programming model. Developers can quickly iterate and see the changes reflected in real-time. Additionally, Svelte's approach to code reuse and component libraries further enhances developer productivity.
React, with its extensive ecosystem and well-established patterns, allows developers to leverage a vast collection of reusable components and tools. Code reuse and community-driven libraries contribute to increased productivity, especially for large-scale projects.
State Management: Svelte vs React
State management in Svelte:
Svelte introduces the concept of stores for state management. Stores are reactive data containers that allow components to share and observe state changes. By utilizing reactive assignments, Svelte handles shared state between components efficiently. Additionally, developers can explore third-party libraries like Redux or Mobx for more advanced state management scenarios.
State management in React:
React primarily relies on local component state for managing state within components. Components receive data through props, which are immutable. React's component hierarchy facilitates the flow of data and state between components. For more complex state management scenarios, developers often integrate external libraries like Redux or Mobx.
Community and Ecosystem: Svelte vs React
Svelte's growing community:
Svelte has been gaining traction and adoption among developers due to its innovative approach and performance benefits. The growing community is actively contributing to the ecosystem, creating learning resources, and organizing Svelte conferences and events. This flourishing community ensures that developers have access to support and up-to-date information.
React's established community:
React boasts an established community that has played a crucial role in shaping the framework. With a strong focus on developer experience, React offers extensive support through various forums, documentation, and online communities. React-specific conferences and meetups provide opportunities for knowledge-sharing and networking within the community.
Tooling and Integration: Svelte vs React
Svelte's tooling ecosystem:
Svelte's tooling ecosystem includes specific development tools like the Svelte REPL, which allows developers to experiment and prototype directly in the browser. Integration with popular integrated development environments (IDEs) like Visual Studio Code enhances the development experience. Svelte also provides testing and debugging utilities for smooth development workflows.
React's tooling ecosystem:
React's tooling ecosystem offers a range of development tools. The React Developer Tools browser extension provides developers with insights into component hierarchies and state. Popular IDEs such as Visual Studio Code, WebStorm, and Atom offer extensive support for React development. Additionally, React has a wide range of testing frameworks and utilities, allowing developers to ensure the stability and quality of their applications.
Performance and Scalability: Svelte vs React
Performance benchmarks of Svelte:
Performance benchmarks demonstrate Svelte's efficiency. Comparisons of render times and memory usage reveal Svelte's lightweight nature and fast runtime. Svelte excels in handling large-scale applications by optimizing performance through its compiler-based approach. Developers can further optimize performance by employing techniques such as code splitting and lazy loading.
Performance considerations in React:
React's performance is impacted by the virtual DOM reconciliation process, which ensures efficient updates. Developers should be mindful of potential bottlenecks and leverage performance optimizations, such as memoization, to minimize unnecessary re-renders. Scaling React applications involves careful management of component hierarchy, state, and data flow to maintain optimal performance.
Use Cases and Real-World Examples: Svelte vs React
Ideal use cases for Svelte:
Svelte is well-suited for various scenarios, including prototyping and small to medium-sized projects. Its lightweight runtime and efficient rendering make it a strong contender for building interactive web applications. Svelte's animation capabilities also make it an excellent choice for creating interfaces with rich animations and transitions.
Ideal use cases for React:
React shines in large-scale applications where scalability and maintainability are crucial. It excels in scenarios that require server-side rendering (SSR) for better performance and search engine optimization (SEO). React is also a popular choice for developing progressive web apps (PWAs) and native mobile applications using frameworks like React Native.
Making the Right Choice
Factors to consider when choosing between Svelte and React
When selecting between Svelte and React, project requirements and constraints should be the primary consideration. Assess factors like performance needs, project complexity, and scalability requirements. Developer familiarity and expertise in a particular framework should also be taken into account. Additionally, evaluating the community support and available resources for each framework can help make an informed decision.
Summary of the pros and cons of Svelte and React:
Svelte offers a unique compiler-based approach, resulting in lightweight and performant applications. Its reactive programming model and component-based architecture promote code organization and reusability. However, Svelte's relatively new status might lead to a smaller community and fewer available resources compared to React.
React, on the other hand, boasts an extensive ecosystem, a large community, and robust community support. Its virtual DOM approach and component reusability contribute to efficient updates and scalability. However, React's performance can be impacted by the virtual DOM reconciliation process, and its learning curve might be steeper for developers new to the JSX syntax and component lifecycle.
Selecting the Best Framework for Your Project
Evaluate your project requirements, consider the learning curve, and assess the community support and resources available for each framework.
React has a larger and more established community, which means you may find more React developers in the job market. Svelte, being a relatively newer framework, might have a smaller pool of available developers. Consider the time and effort required to find and hire developers with the desired skill set.
If you’re pressed for time and would like to supercharge your hiring cycle, consider working with tech partner such as trio to find senior React developers that can get more done.
By carefully weighing these factors, you can make an informed decision and select the framework that best aligns with your project goals, leading to a successful development journey.
7 min read