10-Months Experienced @React Engineer's Mock Interview ❌ Why she Rejected in Tekion Interview

Summary

In this engaging interview, a developer with 9-10 months of experience discusses React fundamentals, asynchronous state updates, and efficient data handling. Key topics include the use of React hooks like `useState` and `useEffect`, with a focus on how state updates are batched and the challenges of managing real-time features like infinite scrolling and video calls. The interviewer provides valuable feedback on problem-solving, encouraging viewers to approach coding challenges with deeper analytical thinking. The video also explores system design principles and practical coding techniques, offering insights for junior and mid-level developers.

Takeaways

• 😀 React's `useState` and `useEffect` hooks are fundamental for managing state and side effects in functional components.
• 🤔 Understanding React’s asynchronous nature is critical, as state updates through `useState` do not happen immediately.
• 📊 React state updates are batched for performance, which can lead to unexpected behavior if not properly handled.
• 🔄 The `useEffect` hook is ideal for managing side effects after rendering, but its behavior depends on the dependency array.
• 🔧 Closures in JavaScript can capture variable values and cause issues when working with asynchronous code like `setTimeout` or `setInterval`.
• 🛠 React developers should always consider edge cases when handling asynchronous code to avoid bugs in the application.
• 🔍 When dealing with infinite scrolling in social media apps, consider memory usage and efficient data storage methods to prevent performance issues.
• 📐 Linked lists can be a useful data structure for dynamic data storage, particularly when dealing with large datasets in infinite scrolling implementations.
• 📱 Building mobile apps with React Native requires handling multiple app states (foreground, background, locked screen) across both Android and iOS platforms.
• 📈 Interviewers often include trick questions, so it's important to thoroughly think through simple questions, as there may be hidden complexities or optimizations.
• ⚡ Focus on both practical and theoretical aspects of development during an interview, such as optimizing React components and understanding system-level decisions like state management and data flow.

Q & A

What is the purpose of the `useState` hook in React?

The `useState` hook in React is used to manage state in functional components. It allows a component to hold and update state values, which will trigger a re-render of the component whenever the state changes.

How does `useEffect` work in React, and when should it be used?

`useEffect` is used for side effects in React functional components. It runs after the render and can be used to fetch data, update the DOM, or subscribe to events. It should be used when you need to perform actions like data fetching, subscribing to external services, or manually updating the DOM.

What happens when multiple `useEffect` hooks are used in a React component?

When multiple `useEffect` hooks are used in a React component, they execute independently of each other. The effects run sequentially after the component renders, and React guarantees that each effect runs after the render phase is complete.

Why does React batch state updates, and how does it affect rendering?

React batches state updates to optimize performance and prevent unnecessary re-renders. When multiple state updates occur in the same event handler, React groups them together, performing a single re-render. This helps improve the overall performance of applications.

What is a closure in JavaScript, and how does it relate to asynchronous operations like `setTimeout`?

A closure in JavaScript is a function that retains access to its lexical scope, even after the outer function has returned. In asynchronous operations like `setTimeout`, closures allow callbacks to remember and access variables from the scope in which they were created, leading to potential issues with state updates if not managed carefully.

In the context of React, why is it important to handle state updates correctly with hooks like `useState` and `useEffect`?

Handling state updates correctly with hooks like `useState` and `useEffect` is important to ensure that components behave as expected. Improper use can lead to issues like state not updating correctly, re-renders happening too frequently, or side effects causing performance problems. Understanding React’s render cycle and how to properly manage state is key to creating efficient and bug-free applications.

What are the challenges of implementing infinite scrolling in a social media app, and how can it be solved efficiently?

Implementing infinite scrolling in a social media app can be challenging because it requires handling large amounts of data that are dynamically loaded as the user scrolls. Storing data efficiently is crucial to avoid performance issues. One solution is to use a linked list to store the data, as it doesn't require continuous memory allocation and allows easy backtracking through previous content.

What factors must be considered when building a video call feature in React Native, and why?

Building a video call feature in React Native requires handling multiple app states (foreground, background, locked, killed) on both Android and iOS. It's important to ensure that video calls continue working correctly in all app states and that the user experience is seamless, even when the app is in the background or the screen is locked. This involves writing native code to manage these lifecycle states.

How does React handle state updates, and why does `setState` in React sometimes appear asynchronous?

React handles state updates by batching them together for performance optimization. `setState` appears asynchronous because React does not immediately update the state after a call. Instead, it schedules the update and performs it during the next render cycle. This ensures that state updates do not block the main thread, leading to smoother performance.

What should developers keep in mind when approaching system design problems from a developer’s perspective?

When approaching system design problems, developers should think about how the system will scale, how resources will be allocated efficiently, and how to handle edge cases. It's important to consider performance optimization, memory usage, and how the system will behave under load. Looking at products like Facebook or Instagram can provide insight into how large-scale systems solve these challenges.