Core Questions

• What are Preload, Reconnect, Prefetch, and Prerender?
• How can you do caching on a website?
• What are ETag, Cache-Control, and Document Fragment?
• How do you optimize assets? What is image compression? What’s the difference between WebP, PNG, and JPG?
• What is a Memory Leak?
• What’s the difference between Repaint and Reflow (often confused with Rework)?
• If a user clicks a button multiple times to fetch data, how to cancel old API calls and use only the latest result?
• Does React use Promise.allSettled() for parallel API calls? How does that work internally?
• What algorithm does Array.prototype.sort() use? What’s the output of [1, null, 5, 2, undefined]?
• What happens when we hit a URL in the browser? What is CRP (Critical Rendering Path)?
• What events can we use when a website is loading? In-depth view of CRP (Critical Rendering Path)
• Difference between Prototypal and Classical Inheritance in JavaScript
• How does JavaScript handle asynchronous operations? What mechanisms does it use?
• What are the SOLID Principles?
• How do we use OOP in JavaScript?
• What are Semantic HTML Elements?
• What is srcset in HTML?
• Difference between display: none and visibility: hidden
• Basic performance-related common questions.
• What is the use of the new operator in JavaScript?
• Explain the webpack build process?
• How would you architect an application to support multiple devices?
• What is the use of Headers in HTTP requests?
• What are render-blocking resources?
• Event Capturing vs Delegation vs Bubbling
• Can we bind this in an arrow function? What happens if we use the new operator with an arrow function?
• Difference between map and object in JavaScript
• What are Closure, Event Loop, Hoisting, and Currying?
• What are Web Core Vitals? How to improve them?
• Explain Web Performance Metrics