JavaScript Performance: Understanding Async and Web Workers

𝗧𝗼𝗽 𝗙𝗿𝗼𝗻𝘁𝗲𝗻𝗱 𝗜𝗻𝘁𝗲𝗿𝘃𝗶𝗲𝘄 𝗤𝘂𝗲𝘀𝘁𝗶𝗼𝗻𝘀 Whether you're preparing for your next big opportunity or mentoring others, this list can be a game-changer. 𝗝𝗮𝘃𝗮𝗦𝗰𝗿𝗶𝗽𝘁 𝗯𝗮𝘀𝗲𝗱 𝗤𝘂𝗲𝘀𝘁𝗶𝗼𝗻𝘀 1. Implement `Promise.all` polyfill 2. Implement `Promise.any` polyfill 3. Implement `Array.prototype.reduce` polyfill 4. Implement Lodash’s `flatten` method 5. Implement auto-retry for promises 6. Throttle promises by batching 7. Debouncing implementation 8. Throttling implementation 9. Execute N callback-based async tasks in series 10. Output prediction for tricky 10–15 JavaScript snippets 11. Object vs Map differences in JavaScript 12. Difference between `PATCH` and `PUT` 13. What is the difference between debounce and throttle? 14. How does the JavaScript Engine work? 15. What is the Event Loop and how does the Microtask Queue work? 16. Explain Virtual DOM and its comparison mechanism 17. How to control tab order in DOM (explain `tabIndex`) 18. What is Event Capturing and Bubbling 19. How to override `toString` on `String.prototype` 20. What is OAuth and how does it work? 21. How does SSO work? 22. What are REST API methods and their differences? 23. Principles of Functional Programming 24. What are microservices? 𝗥𝗲𝗮𝗰𝘁-𝗦𝗽𝗲𝗰𝗶𝗳𝗶𝗰 𝗤𝘂𝗲𝘀𝘁𝗶𝗼𝗻𝘀 1. Why do keys matter in React and how do they improve performance? 2. Explain how `useState` works internally 3. Implement a basic version of `useState` 4. What are React Portals? How are modals mounted using them? 5. What are Error Boundaries in React? 6. How does memoization work in React? 7. SSR vs CSR with examples and use-cases 8. What is Module Federation? 9. What is Micro-Frontend Architecture? 10. Server-Side Rendering techniques to improve SEO 11. What are memory leaks in React and how to detect them? 12. How to measure performance in a React application? 13. How would you build a tool like Create React App? 14. How do you structure reusable UI components in React? Follow Mohamed Irfaan for more related content! 🤔 Having Doubts in technical journey? 🚀 DM to book 1:1 session with me #JavaScript #WebDevelopment #ReactJs #InterviewQuestions #Fundamentals #FrontendDeveloper

#js #8 **Why JavaScript Is Single Threaded Synchronous Language** 🧠 Statement: 👉 “JavaScript is single-threaded and synchronous” We’ll break this into parts so it’s easy to understand. 🧵 1. What is Single-Threaded? 👉 JavaScript has only ONE main thread That means: One call stack One task at a time Example: console.log("A"); console.log("B"); console.log("C"); 👉 Output: A B C ✔ It runs one by one, not in parallel. ⚙️ Why JavaScript is single-threaded? Originally designed for browsers. Browsers (like Google Chrome) need to: Update UI Handle clicks 👉 If multiple threads changed UI at same time: UI would break Data would be inconsistent ✔ So JavaScript uses one thread → safe & predictable ⏱️ 2. What is Synchronous? 👉 Synchronous means: Code runs line by line, and each line waits for previous one to finish Example: console.log("Start"); function slowTask() { for (let i = 0; i < 1; i++) {} } slowTask(); console.log("End"); 👉 Output: Start End (after delay) ✔ End waits until slowTask finishes 🔴 Problem with synchronous nature If something takes time: Everything stops ⛔ UI freezes 👉 Bad user experience 🔄 3. Then how does JavaScript handle async? Here’s the important twist 👇 👉 JavaScript is: ✔ Single-threaded ✔ Synchronous (by default) ❗ BUT supports async using system outside JS 🌐 Behind the scenes JavaScript uses: Browser APIs Event system → Event Loop 📦 Example console.log("Start"); setTimeout(() => { console.log("Async"); }, 2000); console.log("End"); 🔄 Execution flow Start → runs setTimeout → sent to browser End → runs immediately After 2 sec → callback comes back Event loop executes it Output: Start End Async 👉 So JS looks async, but actually: It delegates work Still runs one task at a time 🧑🍳 Simple analogy You (JS) 👨🍳: Cook one dish at a time (single-threaded) Follow order (synchronous) Ask assistant to do waiting tasks (async) 👉 JavaScript is: ✔ Single-threaded One task at a time ✔ Synchronous (by default) Executes line by line ✔ Non-blocking (with help) Uses event loop + browser APIs 👉 JavaScript is single-threaded and synchronous, but uses the event loop to handle asynchronous operations without blocking execution. #Javascript #ObjectOrientedProgramming #SoftwareDevelopment

https://lnkd.in/dA_cAjBs — I used to think I knew React, until I realized I was just writing code that 'worked' but didn't scale. 💡 As a Senior Frontend Engineer, I’ve seen how the definition of a "modern baseline" for TypeScript and React.js has shifted drastically in just the last year. 🔍 I remember a project where we relied on a generic boilerplate that looked great on GitHub. Two months in, the bundle size was a nightmare and the TypeScript types were just 'any' in disguise. 😅 That experience changed how I approach engineering deep-dives. For Part 96 of my React series, I focused on the shifts that actually matter for high-performance apps. ✨ We aren't just looking at basic components anymore. We are talking about leveraging React 19 features alongside Tailwind CSS for maintainable styling. 💎 I spent weeks documenting how to move from messy state logic to clean TanStack Query implementations. 🚀 Plus, why Vite and Storybook have become my non-negotiable duo for rapid prototyping. Testing is another area where people cut corners. I break down how to use Testing Library to ensure your logic actually holds up in the wild. 🛠️ This 5000-word guide is for the developer who is tired of basic tutorials. It’s for the engineer who wants to master the boilerplate React patterns and complex chart js with react integrations used at scale. 📈 What is one React pattern you used to love but now consider an anti-pattern? #FrontendEngineer #TypeScript #ReactJS #WebDevelopment #JavaScript #React19 #TailwindCSS #TanStackQuery #Vite #Storybook #TestingLibrary #SoftwareEngineering #Coding #WebDev #Programming #FrontendEngineers #ReactTips #ReactHooks #TypeScriptTutorial #NextJS #WebPerformance #ModernWeb #SoftwareArchitecture #CodeQuality #DeveloperExperience #FullStack #SoftwareDeveloper #TechCommunity #ReactDeveloper #BoilerplateReact #ChartJS #ReactTestingLibrary #BestReactCourse #ReactComponent #ReactServerComponents #AgGrid #UseState #ReactTutorial #TypeScriptAdvanced #TypeScriptInterview #TSX #ReactNative #ReactTesting #WebDesign #UIUX #CleanCode #ScalableWeb #TechBlog #Harshal #FrontendArchitecture #StateManagement #UnitTesting #ReactPatterns #WebStandard #ES6 #JavaScriptDeveloper #FrontendDevelopment #DevLife #OpenSource #CodingBootcamp #LearnToCode #ProgrammingTips #WebApps #AppDevelopment #SoftwareDesign #WebTech #TechNews #EngineeringExcellence #ComponentLibrary #ResponsiveDesign #FrontendTips #CodeOptimization #JSFrameworks #EnterpriseSoftware #CareerInTech

⚛️ Most React Developers Use Fiber Daily But Don’t Understand It Internally 🫠 Ever wondered how React keeps complex UIs responsive during heavy updates? The answer is React Fiber — React’s internal reconciliation engine introduced in React 16 to improve rendering performance and enable smarter scheduling. ◉ What is React Fiber? React Fiber is a complete rewrite of React’s rendering algorithm. Instead of processing the entire component tree in one blocking operation, React breaks updates into smaller units of work called Fibers. Each Fiber node stores information like: ◆ Component type ◆ Props and state ◆ Parent / child / sibling references ◆ Pending updates ◆ Priority level This gives React the ability to pause, resume, reorder, or cancel rendering work when needed. ◉ Why Older React Had Limitations Before Fiber, React used synchronous recursive rendering. That meant: ✖ Entire tree rendered in one go ✖ Large updates could block the main thread ✖ UI could lag in complex applications ◉ What Fiber Improves With Fiber, React can: ✔ Break rendering into smaller tasks ✔ Prioritize urgent updates ✔ Pause non-urgent work ✔ Resume later efficiently ✔ Keep UI responsive ◉ Example function App() { const [text, setText] = React.useState(""); const [list, setList] = React.useState([]); const handleChange = (e) => { setText(e.target.value); const bigList = Array.from( { length: 10000 }, (_, i) => e.target.value + i ); setList(bigList); }; return ( <> <input onChange={handleChange} /> {list.map(item => <p key={item}>{item}</p>)} </> ); } In this case, Fiber helps React keep typing smooth while handling heavy rendering work in the background. ◉ Two Main Phases ➊ Render Phase Builds the new Fiber tree. Can pause or resume. ➋ Commit Phase Applies DOM updates, effects, refs, and lifecycle changes. ◉ Why It Matters React Fiber enables modern React features such as: ⚡ Concurrent rendering ⚡ Suspense ⚡ startTransition() ⚡ Better responsiveness ⚡ Improved performance in large apps ◉ Simple Analogy Old React: Complete everything at once. Fiber: Break work into tasks and process based on priority. ◉ Final Thought React performance is not only about Virtual DOM. The real power comes from Fiber intelligently scheduling rendering work. #React #JavaScript #Frontend #WebDevelopment #ReactJS #Performance #Coding #SoftwareEngineering

The frontend landscape in 2026 has moved far beyond just "making things look pretty." With the rise of AI-driven interfaces and the demand for ultra-high performance, being a frontend developer today requires a mix of engineering discipline and creative problem-solving. If you are looking to master the frontend and stay ahead of the curve this year, here is the definitive roadmap: 1. Beyond the Basics: Advanced TypeScript 🟦 In 2026, plain JavaScript is rarely enough for professional-grade applications. Mastery of TypeScript—specifically advanced patterns like Generics, Discriminated Unions, and Utility Types—is essential for building bug-free, scalable codebases. The industry has effectively moved to a "Type-first" development cycle. 2. The Meta-Framework Default (Next.js & Beyond) ⚛️ The era of manual bundler configuration is largely over. Meta-frameworks are now the standard: - Next.js & Server Components: Understanding the boundary between Server and Client components is crucial for SEO and performance. - The React Compiler: In 2026, the stable React Compiler automates optimizations like memoization (useMemo, useCallback) that used to take manual effort. - Alternative Runtimes: Mastery of Vite or Bun for lightning-fast development workflows. 3. Mastering the "New" CSS 🎨 CSS has evolved more in the last two years than in the previous ten. - Tailwind CSS: Still the industry standard for rapid styling, but now often paired with native CSS features. - Modern Features: Master Container Queries, Subgrid, and CSS Variables to build truly fluid layouts without heavy JavaScript. - Headless UI: Proficiency in libraries like Radix UI or Shadcn/UI to build accessible, custom-themed components. 4. Performance & Core Web Vitals ⚡ A Senior Frontend Developer is obsessed with speed. - Interaction to Next Paint (INP): This is now the primary metric for responsiveness. - Edge awareness: Learning to run code closer to users via Edge Functions (Vercel/Cloudflare) to cut latency. - Image Optimization: Moving beyond WebP to AVIF for superior compression. 6. The "Backend-ish" Frontend 🌐 The line between frontend and backend is blurring. With server functions and managed data layers, frontend teams are owning more of the stack. Understanding how to design features that handle data-fetching and caching (using TanStack Query or Signals) is a core senior skill. Final Thoughts: The best frontend developers in 2026 aren't just "coders"—they are Product Engineers. They understand user experience, performance budgets, and how to leverage AI to build faster and smarter. Are you doubling down on React this year, or are you exploring new territories like Svelte or Qwik? Let’s discuss in the comments! 👇 #FrontendDevelopment #ReactJS #TypeScript #NextJS #WebDevelopment #FrontendRoadmap2026 #TailwindCSS #UserExperience #SoftwareEngineering #AI #TechTrends

🚀 Closure in JavaScript — Explained Like a Senior React Developer Closures are one of those concepts that look simple… but power some of the most critical patterns in React ⚡ 👉 What is a Closure? A closure is when a function remembers variables from its outer scope, even after the outer function has finished execution. 💡 In short: Function + Lexical Scope = Closure --- 🔹 Basic Example function outer() { let count = 0; return function inner() { count++; console.log(count); }; } const counter = outer(); counter(); // 1 counter(); // 2 👉 Even though outer() is done, inner() still remembers count That’s the power of closure. --- 🔹 Why Closures Matter in React? Closures are everywhere in React: ✔️ Hooks (useState, useEffect) ✔️ Event handlers ✔️ Async operations (setTimeout, API calls) ✔️ Custom hooks --- 🔹 Real-world React Problem: Stale Closure ⚠️ setCount(count + 1); setCount(count + 1); ❌ Both use the same old value of count ✅ Correct approach: setCount(prev => prev + 1); setCount(prev => prev + 1); 👉 This avoids stale closure and ensures latest state is used --- 🔹 Where Closures Help ✅ Data encapsulation (private variables) ✅ Memoization & performance optimization ✅ Debouncing / throttling ✅ Custom hooks ✅ Cleaner state management --- 🔥 Pro Insight (Senior Level) Closures are the backbone of React’s functional paradigm. Misunderstanding them can lead to bugs in: useEffect dependencies Async logic Event callbacks --- 💬 One-line takeaway 👉 “Closures allow functions to retain access to their scope — making React hooks and async logic work seamlessly.” --- #JavaScript #ReactJS #Frontend #WebDevelopment #Programming #InterviewPrep #SoftwareEngineering

https://lnkd.in/dVNHkwV2 — If you're a Frontend Engineer, you know the difference between a "working" UI and a "robust" one is often hidden in the TypeScript types. I’ve spent the last few weeks diving into how we bridge the gap between complex CSS layouts and type-safe components. Last year, I broke a production dashboard because of a z-index conflict with a `css fixed` element that wasn't properly typed in our design system 🚀. It was a humbling moment that reminded me why even "basic" CSS properties need a strict architectural approach if you want to scale. To become a top 1% engineer, you can't just copy-paste from Tailwind CSS or shadcn/ui docs without understanding the underlying mechanics 💡. You have to understand how React 19 handles refs and how Next.js 15 optimizes layouts for the modern web. This 5,000-word guide is part 15 of my journey to document every edge case—from `css first of type` selectors to optimizing data fetching with TanStack Query 🛠️. We're moving towards a world where Vite makes builds instant, but our code quality often still lags behind. Real mastery is knowing exactly how `css flex gap` behaves across mobile browsers while maintaining a perfectly clean, type-safe codebase 🏗️. I wrote this for the engineers who aren't satisfied with "it works on my machine" and want to master the craft 📈. Whether you are handling `css margin top` logic or complex state, the goal is the same: Predictability 🎨. Mastering these nuances is what separates the senior talent from the rest of the pack 💻. What's the one CSS property that consistently gives you a headache in TypeScript projects? ✅ Drop your thoughts below! #FrontendEngineer #TypeScript #ReactJS #NextJS #WebDevelopment #Coding #Programming #SoftwareEngineering #CSS #TailwindCSS #JavaScript #Frontend #WebDev #UIUX #SoftwareDeveloper #CleanCode #React19 #NextJS15 #Vite #TanStackQuery #ShadcnUI #WebDesign #DevCommunity #LearnToCode #CodeNewbie #FullStack #TechTrends #SoftwareDevelopment #SeniorEngineer #EngineeringManager #WebPerformance #DesignSystems #ComponentLibrary #OpenSource #GitHub #TechStack #ModernWeb #CodingLife #Programmer #DigitalNomad #RemoteWork #CareerInTech #TechTips #WebStandards #HTML5 #CSS3 #ES6 #PerformanceOptimization #SystemDesign #SoftwareArchitecture #CSSTricks #TypeScriptTips #ReactTips #FrontEndDev #FullStackDeveloper #JuniorDeveloper #MidLevelDeveloper #StaffEngineer #PrincipalEngineer #FrontendEngineers #CodingBestPractices #BuildInPublic #SaaS #SoloFounder #IndieHackers #TechStartup #WebApps #AppDevelopment #ProductEngineering #Debugging #CodeQuality #DeveloperExperience #DX #SoftwareTesting #DevOps

https://lnkd.in/dpSkdGET — Most senior devs are still writing JavaScript like it’s 2018, and it is quietly killing your app's performance. As a Senior Frontend Engineer working with TypeScript and React 19 daily, I’ve realized that the "standard" way of doing things is often outdated. I just released Part 98 of The Modern JavaScript Playbook—a massive 5,000+ word deep dive into the evolution of our ecosystem. While researching this piece, I found a surprising "modern baseline" shift. 💡 We often focus on 'includes javascript' logic or 'javascript if not' patterns for functional safety. But we’re ignoring how modern engines handle closures and memory during complex page transitions. I remember spending an entire weekend debugging a janky scroll animation on a production site. The culprit? A memory leak inside a hook that I thought was "standard" practice. 🧠 That mistake taught me that even with fast tools like Vite and Bun, our code patterns are the real bottleneck. In this playbook, I break down advanced design patterns, async/await pitfalls, and how to use Framer Motion with Tailwind CSS without destroying your frame rate. ⚡ It’s the comprehensive guide I wish someone had handed me when I started scaling frontend systems. 🛠️ It's time to move beyond basic tutorials and master the engineering behind the code. 📈 What is the one JavaScript concept that took you the longest to truly master? 🚀 #FrontendEngineer #TypeScript #ReactJS #JavaScript #WebDevelopment #SoftwareEngineering #Coding #Programming #FrontendEngineers #NextJS #WebPerf #CleanCode #JavaScriptTips #TechCommunity #SoftwareArchitecture #React19 #FramerMotion #TailwindCSS #ViteJS #BunJS #CodingLife #WebDevTips #JSPlaybook #AdvancedJavaScript #PerformanceOptimization #FullStackDev #ComputerScience #CodeQuality #DeveloperExperience #OpenSource #TechInsights #FrontendDev #WebDesign #UIUX #ModernWeb #SoftwareDev #TechTutorial #ProgrammingTutorial #LearningToCode #CodeNewbie #WebStandard #JavaScriptTutorial #EngineeringManager #TechLeader #SystemDesign #CodeOptimization #AsyncAwait #JavaScriptClosures #DesignPatterns #AnimationPerformance #DOMManipulation #HTML5 #CSS3 #ES6 #TypeScriptTips #WebApps #SoftwareEngineerLife #JuniorToSenior #TechCareer #DevOps #CloudComputing #Vercel #Netlify #GitHub #FrontendArchitecture #SoftwareDesign #CodingSkills #WebTech #TechBlog #Harshal #CodingBestPractices #WebPerformanceTips #JavaScriptBestPractices #ReactTips #UIEngineering

𝗧𝗼𝗽𝗶𝗰 𝟭𝟮: 𝗘𝘃𝗲𝗻𝘁 𝗟𝗼𝗼𝗽 (𝗠𝗮𝗰𝗿𝗼 𝘃𝘀 𝗠𝗶𝗰𝗿𝗼𝘁𝗮𝘀𝗸𝘀) JavaScript is single-threaded, yet it handles thousands of concurrent operations without breaking a sweat. The secret isn't raw speed; it's an incredibly strict, ruthless prioritization engine. If you don't understand the difference between a macro and a microtask, your "asynchronous" code is a ticking time bomb for UI freezes. Summary: The Event Loop is the conductor of JavaScript's concurrency model. It continuously monitors the Call Stack and the Task Queues. To manage asynchronous work, it uses two distinct queues with vastly different priorities: Macrotasks (like setTimeout, setInterval, network events) and Microtasks (like Promises and MutationObserver). Crux: The VIP Queue: Microtasks have absolute priority. The engine will not move to the next Macrotask, nor will it allow the browser to re-render the screen, until the entire Microtask queue is completely empty. The Normal Queue: Macrotasks execute one by one. After a single Macrotask finishes, the Event Loop checks the Microtask queue again. The Starvation Risk: Because Microtasks can spawn other Microtasks, a recursive Promise chain can hold the main thread hostage, permanently blocking the UI from updating. The Deep Insight (Architect's Perspective): Traffic Control and Yielding: As architects, we must visualize the Event Loop as a traffic control system where Microtasks are emergency vehicles. When you resolve a massive chain of Promises or heavy async/await logic, you are flooding the intersection with ambulances. The browser's rendering engine—the normal traffic—is forced to sit at a red light until every single emergency vehicle has cleared. We don't just use async patterns for code readability; we must actively manage thread occupancy. For heavy client-side computations, we must intentionally interleave Macrotasks (like setTimeout(..., 0)) to force our code to yield control back to the Event Loop, allowing the browser to paint frames and keeping the UI responsive. Tip: If you have to process a massive dataset on the frontend (e.g., parsing a huge JSON file or formatting thousands of rows), do not use Promise.all on the entire set at once. That floods the Microtask queue and locks the UI. Instead, "chunk" the array and process each chunk using setTimeout or requestAnimationFrame. This gives the Event Loop room to breathe and the browser a chance to render 60 frames per second between your computation chunks. Tags: #SoftwareArchitecture #JavaScript #WebPerformance #EventLoop #FrontendEngineering #CleanCode

Angular & NestJS: The "Power Couple" of Modern Web Development 🤝 If you are an Angular developer and you are not using NestJS for your backend, you are missing out on some serious productivity! 🚀 As a Full-Stack Developer, I’ve realized that using these two together is like speaking the same language on both ends of the application. Why is this combination so powerful? 1️⃣ Unified Language (TypeScript): No more switching between JavaScript (Node/Express) and TypeScript. You use the same interfaces, classes, and logic across the entire stack. 2️⃣ Shared Architecture: NestJS was heavily inspired by Angular. It uses the same concepts like: Modules for organization. Decorators (@Controller, @Injectable). Dependency Injection (DI) for managing services. 3️⃣ Scalability: Just like Angular is built for large enterprise-grade frontends, NestJS is built for high-performance, maintainable backends. They both follow a "Modular" approach, making it easy to manage complex projects. 4️⃣ Developer Productivity: Context switching is a performance killer. When your Backend looks and feels like your Frontend, you write code faster and with fewer bugs. The Bottom Line: For enterprise-level applications that require structure, discipline, and performance, the Angular + NestJS stack is unbeatable. It’s not just about building a website; it’s about building a scalable system. Are you a fan of this stack, or do you prefer mixing different frameworks for Frontend and Backend? Let's discuss in the comments! 👇 #FullStack #NestJS #Angular #TypeScript #SoftwareArchitecture #BackendDevelopment #WebDev #ProgrammingLife #TechCommunity