Senior React Interview Questions: If You Can’t Answer This, You’re Not Ready

Summary

This video provides 20 advanced React interview questions designed for senior-level developers, covering key concepts like state management, React context, and component behavior. Topics include the purpose of React hooks, the use of tools like Webpack and Parcel, differences between development and production dependencies, and advanced React features like code splitting and lazy loading. The script also dives into React’s internal workings such as reconciliation and the role of controlled vs. uncontrolled components, all geared toward preparing developers for a deeper understanding of React's functionality and performance optimization.

Takeaways

• 😀 Lifting state up in React means moving state from child components to a parent component, enabling shared state management across multiple components.
• 😀 React Context allows you to share data or functions across components, helping you avoid prop drilling, especially in deeply nested component structures.
• 😀 There are multiple ways to add CSS to React applications, including global CSS, inline styles, CSS modules, Tailwind, and CSS-in-JS solutions.
• 😀 Hot Module Replacement (HMR) is a development feature that enables you to see changes without refreshing the page, maintaining the app's state.
• 😀 Tools like Parcel, Vite, and Webpack are used to bundle your app, with Vite being the fastest option, especially for React development.
• 😀 `Create React App` is deprecated, and it is recommended to use Vite for React project setup as it supports faster development and better configurability.
• 😀 Tree Shaking is a process that eliminates unused code from your final bundle, reducing bundle size and improving performance in production.
• 😀 The difference between dependencies and dev dependencies in `package.json` is that dependencies are used in production, while dev dependencies are only for development purposes.
• 😀 `npx` is a command-line tool for executing packages without installing them globally, while `npm` is used to manage and install project dependencies.
• 😀 `package-lock.json` locks all the dependencies and their versions, ensuring that the exact same versions are used every time the app is installed, while `package.json` only lists dependencies without locking their versions.

Q & A

What does 'lifting state up' mean in React?

Lifting state up refers to moving the state from a child component to a parent component in order to share it across multiple components. This centralizes the state management in the parent, allowing child components to interact with it via callbacks.

What is React Context and how does it differ from Angular's services?

React Context allows state or functions to be shared across components without passing props manually at every level. It differs from Angular's services as React doesn't provide a built-in service concept, but rather uses Context API to enable this functionality.

What are some ways to add CSS to a React application?

In React, you can add CSS in several ways: by importing global CSS files, using inline styles as objects, using CSS modules for scoped styles, or employing utility libraries like Tailwind CSS or CSS-in-JS solutions like styled-components.

What is Hot Module Replacement (HMR) in React?

Hot Module Replacement allows you to update components and the state of your app without refreshing the page. It improves the development experience by preserving the application state across code changes.

How do Parcel, Vite, and Webpack relate to building React applications?

Parcel, Vite, and Webpack are build tools that help transpile and bundle your code, manage assets, and enable features like hot reloading and CSS preprocessing. Vite is particularly noted for being faster in development due to its use of ES modules.

What is tree shaking in React?

Tree shaking is a build optimization technique that removes unused code from your JavaScript bundle. It helps reduce the bundle size by excluding code that isn't used in the application, leading to faster load times.

What is the difference between 'devDependencies' and 'dependencies' in package.json?

Dependencies are packages required for your application to run in production, whereas devDependencies are tools used during development (such as testing libraries or build tools) that aren't needed in production.

What is the difference between 'npx' and 'npm'?

'npm' is a package manager used to install dependencies, whereas 'npx' is a package executor that allows you to run packages without installing them globally. It’s useful for running commands like 'create-react-app' without needing to install them first.

What is the purpose of the 'useEffect' dependency array in React?

The dependency array in 'useEffect' controls when the effect is re-executed. If empty, it runs once after the initial render. If it contains variables, the effect runs again only when those variables change, helping optimize component re-renders.

What is the difference between controlled and uncontrolled components in React?

A controlled component is a component where React manages the state of form elements (e.g., input fields) through state hooks like 'useState'. An uncontrolled component, on the other hand, lets the DOM handle the form element's state, often using refs to access the input value later.