Frontend Interview Questions 2024 (Part 2)

Summary

This video offers a comprehensive guide for senior front-end engineers preparing for interviews. It covers the top seven front-end interview questions, including the differences between cookies, local storage, and session storage, performance optimizations, and managing code quality. The video also addresses handling large assets like images, preventing XSS attacks, the workings and benefits of CDNs, and the concept of micro-frontends. It emphasizes the importance of focusing on performance optimization and secondary skills, which are often overlooked but crucial for excelling in technical interviews.

Takeaways

• 🍪 The difference between cookies, local storage, and session storage is highlighted: cookies are limited to 4KB, server and client-side, great for authentication; local storage has a higher limit and persists indefinitely, good for app state; session storage is deleted when the tab is closed, useful for form inputs.
• 🛠️ Front-end performance optimizations include using a module bundler, polyfilling, compression, minification, and code splitting to ensure only necessary JavaScript is loaded initially.
• 📸 Image optimization techniques for large images include resizing to fit the display, compression, using the webp format, leveraging CDNs, and implementing lazy loading.
• 🚀 Performance is a key focus area in front-end interviews, often overshadowing traditional coding skills, emphasizing the need for developers to be proficient in optimization techniques.
• 🔒 Ensuring code quality in large-scale applications involves using linters, unit tests, end-to-end tests, accessibility checks, and dependency scanning.
• 🐛 XSS attacks can be mitigated by sanitizing user inputs and avoiding direct rendering of user-supplied HTML or JavaScript in the frontend.
• 🌐 CDNs work by replicating website assets across a network of servers, serving content from the closest location to the user, which improves load times and reduces latency.
• 🏢 Micro frontends involve splitting a large monolithic frontend application into smaller, independent applications, which can be developed and deployed separately, but this approach adds complexity and is best suited for large teams.
• 💡 The decision to adopt micro frontends should be based on organizational needs, team size, and the desire to improve development speed and parallelism, rather than being driven by technology trends alone.
• 👨‍🏫 Mentorship is emphasized as a key factor in career advancement for developers, with the offer for personal mentorship to help developers become more confident and reach senior positions.

Q & A

What is the primary difference between cookies, local storage, and session storage in a browser?

Cookies are limited to about 4KB, are sent with every HTTP request, and are great for authentication and sharing state between server and client. Local storage has a much higher limit and persists indefinitely, making it ideal for storing application state that needs to be retained even after the browser is closed. Session storage is similar to local storage but is cleared when the browser tab or window is closed, which is useful for storing temporary data like form inputs.

What are some optimizations to implement for a new front-end application to enhance its performance?

Optimizations include using a module bundler like Webpack, polyfilling to support modern JavaScript features in older browsers, applying compression to reduce file size, minifying and uglifying code for smaller payloads, and using source maps for debugging. Additionally, code splitting to reduce initial load time, implementing CDN for faster content delivery, optimizing images, and using lazy loading for non-critical resources are also recommended.

How do you explain the concept of polyfilling in the context of front-end development?

Polyfilling involves adding code to a base application to provide modern JavaScript features for browsers that do not natively support them. This ensures that all users have a consistent experience regardless of the browser they are using.

What is tree shaking and how does it relate to front-end performance optimization?

Tree shaking is a technique used by module bundlers to remove unused code from the final bundle. This reduces the file size and improves the application's load time, which is crucial for performance optimization.

How can you optimize images for a high-definition front-end application like an eCommerce store?

Optimizations include ensuring the image dimensions match the display size to avoid unnecessary scaling, compressing images to reduce file size without compromising quality, using modern formats like WebP for better compression, hosting images on a CDN for faster delivery, and implementing lazy loading to load images only as they enter the viewport.

What is the significance of using a CDN in front-end development, and what are some popular providers?

A CDN (Content Delivery Network) improves performance by serving content from servers closest to the user, reducing latency and load times. Popular CDN providers include AWS CloudFront, Cloudflare, and Azure CDN.

How do you manage code quality in a large-scale front-end application?

Managing code quality involves using linters for style consistency, setting up unit and end-to-end tests for functionality, performing dependency scans for security, and possibly integrating tools like Lighthouse or Sentry for monitoring performance and accessibility.

What is an XSS attack, and how can you protect a front-end application from it?

An XSS (Cross-Site Scripting) attack occurs when an attacker manages to inject malicious scripts into content that other users see. Protection involves sanitizing user input to prevent malicious code from being stored, and avoiding the direct rendering of user-supplied content on the front end.

Can you briefly describe how a CDN works and its advantages?

A CDN works by replicating website assets across a network of servers globally. When a user requests content, they are directed to the server with the lowest latency, which serves the content. This reduces load times and improves user experience. Advantages include faster content delivery, reduced server load, and improved site reliability.

What are micro-frontends, and when would you consider using this architecture?

Micro-frontends are a architectural pattern where a large application is broken down into smaller, independent front-end applications that can be developed, deployed, and scaled separately. This approach is beneficial for large teams working on complex projects, as it allows for parallel development and can improve deployment efficiency, though it introduces additional complexity.