# Under The Hood

Under The Hood is a technical publication by Srikar Phanikumar Marti covering frontend internals, browser behavior, JavaScript, React, web performance, accessibility, and AI engineering.

Canonical site: https://blog.mspk.me
RSS feed: https://blog.mspk.me/rss.xml

## Use

Use the canonical post URLs when citing or summarizing this publication. Prefer the article title, URL, and publication context over platform syndication copies.

## Recent Posts

- [New Newsletter Alert: Under The Hood Has a New Home](https://blog.mspk.me/posts/new-newsletter-alert)
  Summary: Why I moved from Substack to an owned newsletter, how I ported the archive, and what I am building from here.
  Tags: newsletter, substack, publishing, nextjs
- [Optimizing React Suspense: How Concurrent Mode Handles Data Fetching and Rendering](https://blog.mspk.me/posts/optimizing-react-suspense-how-concurrent-mode-handles-data-fetching-and-rendering)
  Summary: Ever seen your React Suspense fallback flash briefly, then disappear, then maybe reappear? Let’s unravel what’s really going on under the hood with React Concurrent Mode’s update prioritization, Suspense boundaries, and data fetching. Understanding this can help you fine-tune your loading UX and boost perceived performance.
  Tags: React, Suspense, Concurrent Mode, Performance, Frontend, ReactInternals
- [React Server Components: Under the Hood of Streaming and Client Boundaries](https://blog.mspk.me/posts/react-server-components-under-the-hood-of-streaming-and-client-boundaries)
  Summary: Ever wondered how React Server Components stream content to your app and keep client and server logic neatly separated? Let me walk you through the guts of this feature, based on my own debugging and experimentation.
  Tags: React, Server Components, Streaming, FrontendArchitecture, WebDev
- [The Accessibility Tree: What Your DOM Doesn’t Tell You About Screen Readers](https://blog.mspk.me/posts/the-accessibility-tree-what-your-dom-doesn-t-tell-you-about-screen-readers)
  Summary: Dissect the accessibility tree construction from DOM and CSS, how browsers expose it to assistive tech, and debugging mismatches between UI and accessibility APIs.
  Tags: Accessibility, DOM, ScreenReaders, WebDev, Debugging
- [What will-change Actually Does to Your GPU Memory](https://blog.mspk.me/posts/what-will-change-actually-does-to)
  Summary: At some point you hit a janky animation, Googled the fix, and found a Stack Overflow answer that said add will change: transform to the element. You added it. The animation got smoother. You moved on. Most developers sto
  Tags: Substack
- [Hydration Isn't Magic — Here's the Exact Sequence That Breaks It](https://blog.mspk.me/posts/hydration-isnt-magic-heres-the-exact)
  Summary: If you have used Next.js, Nuxt, Remix, or any server rendered React framework, you have almost certainly seen this warning at some point: Warning: Text content did not match. Server: "Hello" Client: "Hello " Or the page 
  Tags: Substack
- [The Scroll Performance Problem CSS Solved That JavaScript Made Worse](https://blog.mspk.me/posts/the-scroll-performance-problem-css)
  Summary: Scroll handlers are one of those things that seem completely reasonable until you understand what actually happens when you attach one. Every time the user scrolls, the browser fires your handler. Not once per frame. Not
  Tags: Substack
- [How the Browser Decides Your Font Is \"Loaded\" ](https://blog.mspk.me/posts/how-the-browser-decides-your-font)
  Summary: You’ve seen it happen. The page loads, text appears in a fallback font, and then a fraction of a second later everything shifts as the real font kicks in. Or worse — the text is invisible for a moment, then pops in. You 
  Tags: Substack
- [Why localStorage Silently Fails in Safari](https://blog.mspk.me/posts/why-localstorage-silently-fails-in)
  Summary: You ship a feature. It works perfectly in Chrome. You test it in Firefox. Still fine. Then someone files a bug that their settings aren’t saving, their preferences reset on every visit, the thing you built just doesn’t w
  Tags: Substack
- [Why typeof null === ‘object’ Is a Bug That Can Never Be Fixed](https://blog.mspk.me/posts/why-typeof-null-object-is-a-bug-that)
  Summary: Open your browser console right now and type this: typeof null It returns "object" . It’s wrong. Everyone knows it’s wrong. The people who built JavaScript knew it was wrong. And it will never be fixed. Here’s the full s
  Tags: Substack
- [How import() Changed Frontend Architecture and (almost) Nobody Noticed](https://blog.mspk.me/posts/how-import-changed-frontend-architecture)
  Summary: We spent years arguing about code splitting. Webpack configs, bundle strategies, route based splitting, component level splitting; entire articles written about how to slice your JavaScript so users don’t download what t
  Tags: Substack
- [The structuredClone You Should Have Been Using Instead of JSON Hacks](https://blog.mspk.me/posts/the-structuredclone-you-should-have)
  Summary: At some point, every JavaScript developer writes this: const copy = JSON.parse JSON.stringify original ; You know it’s ugly. I know it’s ugly. We all wrote it anyway because it worked — until it didn’t. The thing is, JSO
  Tags: Substack
- [Your Service Worker Is Serving Stale Code (And Your Users Are Stuck in a Time Warp)](https://blog.mspk.me/posts/your-service-worker-is-serving-stale)
  Summary: Progressive Web Apps PWAs promised us a beautiful, offline first future. We were told that by implementing service workers, we could bypass the unpredictable volatility of mobile networks, cache our core application shel
  Tags: Substack
- [The rem vs px Illusion: How Browsers Actually Scale Typography for Accessibility](https://blog.mspk.me/posts/the-rem-vs-px-illusion-how-browsers)
  Summary: Go to any frontend engineering forum, search for typography, and you will find yourself staring into a deep, dogmatic rabbit hole. The battle lines were drawn a decade ago: on one side, you have the pixel purists who wan
  Tags: Substack
- [Why I Published an npm Package Just to Parse a String to a Boolean](https://blog.mspk.me/posts/why-i-published-an-npm-package-just)
  Summary: If you want to start a flame war in a room full of JavaScript developers, just bring up type coercion. We’ve all seen the memes. We all know that == evaluates to true , and we’ve all laughed at the bizarre, dark corners 
  Tags: Substack
- [The DistilBERT Ceiling: The Exact Moment You Must Evict Client-Side AI to a Web Worker](https://blog.mspk.me/posts/the-distilbert-ceiling-the-exact)
  Summary: In my last two posts, we looked at how running machine learning models directly in the browser can completely crash your Core Web Vitals, and why a model’s underlying architecture matters far more than its raw parameter 
  Tags: Substack
- [Size Doesn’t Matter: Why a 39M Parameter AI Model Is Slower Than a 110M One in the Browser](https://blog.mspk.me/posts/size-doesnt-matter-why-a-39m-parameter)
  Summary: If you hang around frontend engineering circles long enough, you’ll notice we have a universal rule of thumb for optimization: smaller is better . Smaller bundle sizes mean faster time to interactive. Smaller image asset
  Tags: Substack
- [I Benchmarked Running AI Models Directly in the Browser. It Completely Trashed My Core Web Vitals.](https://blog.mspk.me/posts/i-benchmarked-running-ai-models-directly)
  Summary: We are living in the golden age of offloading computation to the client. Frameworks are faster, edge networks are smarter, and libraries like Transformers.js have made running actual neural networks inside a browser look
  Tags: Substack
- [Your AI Feature Works. Your Users Don't Trust It. Here's Why.](https://blog.mspk.me/posts/your-ai-feature-works-your-users)
  Summary: The gap between \"it's accurate\" and \"I believe it\" is wider than you think — and entirely your fault to close
  Tags: Substack
- [AI Killed \"Powered by AI\"](https://blog.mspk.me/posts/ai-killed-powered-by-ai)
  Summary: The label that was supposed to sell your product is now the reason users don't trust it
  Tags: Substack
- [Designing for Confident Wrong Answers: The Hardest UX Problem in AI](https://blog.mspk.me/posts/designing-for-confident-wrong-answers)
  Summary: The model is wrong. You can tell because you happen to know the answer. But your user doesn’t — and the interface gave them no reason to doubt it. This is the central UX failure in AI products right now. Not that models 
  Tags: Substack
- [You Hated Matrix Math in College. Turns Out It Runs Every AI Model You’ve Ever Used.](https://blog.mspk.me/posts/you-hated-matrix-math-in-college)
  Summary: There’s a specific kind of pain reserved for sitting in a linear algebra lecture, staring at a matrix multiplication problem, and thinking: when will I ever use this? Your professor said “it’s foundational.” You filed th
  Tags: Substack
- [The KV Cache: Why Your API Bill Is Higher Than It Should Be](https://blog.mspk.me/posts/the-kv-cache-why-your-api-bill-is)
  Summary: If you’ve used the Claude or OpenAI APIs at any meaningful scale and never touched prompt caching, you’ve been overpaying. Potentially by 90%. Not as a rounding error — as a structural tax on not understanding what’s hap
  Tags: Substack
- [Fine-Tuning vs. RAG vs. Prompting: Stop Asking Which Is Best](https://blog.mspk.me/posts/fine-tuning-vs-rag-vs-prompting-stop)
  Summary: Every vendor selling fine tuning will tell you fine tuning is the answer. Every vendor selling a vector database will tell you RAG is the answer. Every API provider will tell you prompting is the answer. None of them are
  Tags: Substack
- [Tokens Are Not Words: What Every Developer Building on LLMs Actually Needs to Know](https://blog.mspk.me/posts/tokens-are-not-words-what-every-developer)
  Summary: You’ve been paying for tokens since the day you made your first API call. You know the rough “4 characters per token” heuristic. You’ve probably hit a context limit at least once and scrambled to truncate your prompt. Bu
  Tags: Substack
- [The React prop you use every day and completely misunderstand (Its key)](https://blog.mspk.me/posts/the-react-prop-you-use-every-day)
  Summary: There is a prop in React that every single developer uses, that shows up in almost every component that renders a list, that junior and senior devs alike type without thinking — and almost nobody actually understands wha
  Tags: Substack
- [I built a marketplace of AI tools for 99 cents each. Then I waited for traffic that never came.](https://blog.mspk.me/posts/i-built-a-marketplace-of-ai-tools)
  Summary: Let me tell you about the moment the idea clicked. I needed to summarize a PDF. Nothing exotic — a long report, wanted the key points, didn’t want to read the whole thing. So I went looking for a tool. Found one. Clean U
  Tags: Substack
- [You don’t need a component for that](https://blog.mspk.me/posts/you-dont-need-a-component-for-that)
  Summary: Somewhere along the way, React developers stopped writing HTML. Not literally — the JSX is still there, the tags are still there. But the instinct to reach for a plain <div or a <button or a <p without wrapping it in som
  Tags: Substack
- [Tailwind isn't a CSS framework. It's a CSS avoidance framework. And that's fine.](https://blog.mspk.me/posts/tailwind-isnt-a-css-framework-its)
  Summary: Here’s a sentence that will get me ratio’d on Twitter: most Tailwind developers don’t know CSS. Not “aren’t good at CSS.” Don’t know it. They know flex , items center , gap 4 . They know how to scan a Tailwind docs page.
  Tags: Substack
- [Tree Shaking Doesn’t Work (Most of the Time)](https://blog.mspk.me/posts/tree-shaking-doesnt-work-most-of)
  Summary: You install a library. You import one function. Your bundle grows by 500kb. “But I only used debounce ” you scream at webpack. Webpack shrugs. Lodash is in your bundle. All of it. Every function you didn’t use. Every uti
  Tags: Substack
- [Why 0.1 + 0.2 !== 0.3 (And What To Do About It)](https://blog.mspk.me/posts/why-01-02-03-and-what-to-do-about)
  Summary: Type this into your browser console: 0.1 + 0.2 You get: 0.30000000000000004 Not 0.3 . Not even close. Off by 0.00000000000000004. This isn’t a JavaScript bug. This is how computers work. And it breaks shopping carts, fin
  Tags: Substack
- [JavaScript Has 9 Ways to Check Equality (And They All Disagree)](https://blog.mspk.me/posts/javascript-has-9-ways-to-check-equality)
  Summary: Most languages have one way to check if two things are equal. Maybe two if you’re fancy. JavaScript has nine . And they all give different answers. On the same values. Let me show you the madness. The Basics That Aren’t 
  Tags: Substack
- [JavaScript Has Two Zeros (And One is Negative?)](https://blog.mspk.me/posts/javascript-has-two-zeros-and-one)
  Summary: I’ve been writing JavaScript for over a decade. I thought I understood numbers. Then someone showed me this: 0 === 0 // true\nObject.is 0, 0 // false Wait. What? JavaScript has two zeros. And they’re both zero. But one i
  Tags: Substack
- [$0 and Friends: The DevTools Shortcuts You’re Missing](https://blog.mspk.me/posts/0-and-friends-the-devtools-shortcuts)
  Summary: You’re debugging. You inspect an element. Now you want to test something on it in the console. So you do this: document.querySelector '.some complicated selector you have to type' Or worse, you right click, “Copy selecto
  Tags: Substack
- [Stop Installing Form Libraries. The Browser Can Do This.](https://blog.mspk.me/posts/stop-installing-form-libraries-the)
  Summary: Every React form tutorial starts the same way: npm install react hook form\n or\nnpm install formik\n or\nnpm install yup zod @hookform/resolvers\n Then you write 50 lines of boilerplate to validate an email field. Here’
  Tags: Substack
- [The inert Attribute: Stop Writing Focus Trap JavaScript](https://blog.mspk.me/posts/the-inert-attribute-stop-writing)
  Summary: Every time you build a modal, you write the same JavaScript.
  Tags: Substack
- [Stencil is the Framework Nobody Uses (But Maybe Should)](https://blog.mspk.me/posts/stencil-is-the-framework-nobody-uses)
  Summary: I’ve been building web components with Stencil for years now.
  Tags: Substack
- [JavaScript Finally Fixed Dates (And It Only Took 30 Years)](https://blog.mspk.me/posts/javascript-finally-fixed-dates-and)
  Summary: The Temporal API just shipped in Chrome 144 and Firefox 139. If you’ve ever fought with Date objects, this is the moment you’ve been waiting for. The Date Object Was Always Broken Let me tell you a story. In 1995, Brenda
  Tags: Substack
- [Micro Frontends Failed Because Web Components Failed](https://blog.mspk.me/posts/micro-frontends-failed-because-web)
  Summary: And we’re all pretending Webpack Module Federation is the answer
  Tags: Substack
- [What Happens During a Browser Tab Crash](https://blog.mspk.me/posts/what-happens-during-a-browser-tab)
  Summary: Had a tab freeze completely. Spinning beachball. Couldn’t click anything. Switched to another tab. That one worked fine. Closed the frozen tab. Browser kept running like nothing happened. Ten years ago, that would’ve cra
  Tags: Substack
- [How Browsers Store and Manage Variables in Memory](https://blog.mspk.me/posts/how-browsers-store-and-manage-variables)
  Summary: Changed the order of object properties in my code. Same data, just rearranged. Performance got worse. What? Turns out JavaScript engines care about object shape. Not just what properties you have, but what order you crea
  Tags: Substack
- [Z-Index Isn't a Number, It's a Context](https://blog.mspk.me/posts/z-index-isnt-a-number-its-a-context)
  Summary: Set z index: 99999 on a modal. Still rendered behind a dropdown with z index: 10 . What? Spent 30 minutes incrementing the number. 999999 . 9999999 . Added more nines. Didn’t help. Turns out z index doesn’t work how I th
  Tags: Substack
- [Why onClick={() => doThing()} Is Different from onClick={doThing}](https://blog.mspk.me/posts/why-onclick-dothing-is-different)
  Summary: Reviewed a pull request recently for a local project/demo. One of my friends who is also a contributor to that demo changed all the onClick={doThing} to onClick={ = doThing } . Asked why. They said “that’s how the tutori
  Tags: Substack
- [The Cascade in CSS (Most People Get This Wrong)](https://blog.mspk.me/posts/the-cascade-in-css-most-people-get)
  Summary: Spent years writing CSS before I actually understood the cascade.
  Tags: Substack
- [Why Some Fonts Look Different on Mac vs Windows](https://blog.mspk.me/posts/why-some-fonts-look-different-on)
  Summary: Designed a site on my Mac. Looked great. Opened it on a Windows laptop. Same fonts, completely different appearance. Thinner, sharper, kind of harsh. Thought my CSS was broken. Nope. Just font rendering. The Thing Nobody
  Tags: Substack
- [Should You Still Learn Frontend in the Age of AI?](https://blog.mspk.me/posts/should-you-still-learn-frontend-in)
  Summary: Or: Why understanding how browsers work might be your best career move right now
  Tags: Substack
- [Why Your Favicon Needs So Many Sizes](https://blog.mspk.me/posts/why-your-favicon-needs-so-many-sizes)
  Summary: Added a favicon to a site last week. Thought I was done. Then tested it on my phone. Looked like garbage. Turns out one favicon.ico file isn’t enough anymore. The Thing That Should Be Simple A favicon is just that little
  Tags: Substack
- [You Don’t Need That Library](https://blog.mspk.me/posts/you-dont-need-that-library)
  Summary: Installed a library last week to debounce a function. Then realized I could’ve written it in five lines. Felt a little dumb. The Thing We All Do Problem comes up. Google the problem. Find a library. npm install . Import 
  Tags: Substack
- [preventDefault() vs stopPropagation() vs return false](https://blog.mspk.me/posts/preventdefault-vs-stoppropagation)
  Summary: Over the course of my career, I spent an embarrassing amount of time confused about these three.
  Tags: Substack
- [npm vs npx vs pnpm vs yarn (They’re Not All Doing the Same Thing)](https://blog.mspk.me/posts/npm-vs-npx-vs-pnpm-vs-yarn-theyre)
  Summary: I’ve typed npm install probably ten thousand times.
  Tags: Substack