🧠 React Derived State: The Trick Juniors Miss

A quick note before we get into the newsletter.

Tomorrow morning, Cosden Code goes live 🚀

After weeks of walking you through the platform, the Cosden Assistant, the hands-on coding environment, the ever-evolving curriculum, tomorrow is launch day.

Here's what you're getting:

This is the platform I wish existed when I was learning React. Expert instruction when you need context. Hands-on practice so concepts actually stick. And help available the moment you get stuck.

If you're on the waitlist, keep an eye on your inboxes for early access tonight!

Not on the waitlist yet? You can still join now and get the access link before the public, this is your last chance.

🏃 TanStack Pacer Enters Beta
TanStack has officially released Pacer into beta, following its initial reveal earlier this year. The library provides framework-agnostic utilities for debouncing, throttling, rate limiting, queuing, and batching. It includes type-safe APIs, reactive adapters, and support for both async and sync execution, along with cleanup, cancellation, and error-handling options.

➡ Migrating 6000 React tests using AI Agents and ASTs
This is a good read if you’re curious about how AI handles large-scale, real-world code migrations, not toy demos, but thousands of files in a mature codebase. A Filestage engineer documented migrating 6,000+ React tests from Testing Library v13 to v14 using AI agents + AST codemods, starting with a migration guide, running both package versions in parallel, and iterating on a jscodeshift codemod to cover common patterns.

📱 How Vercel built the v0 iOS app
The Vercel team published a detailed breakdown of how they built the v0 iOS app, covering everything from chat animations and keyboard handling to native patches that make React Native feel truly native. It’s a worthwhile read because it shows the real engineering work behind polished AI chat UIs, things like dynamic blank-size calculations, Liquid Glass composers, staggered streaming text, and custom fixes upstreamed to React Native.

💡 How to Simplify Your React Components with Derived State
This article breaks down derived state in React, showing why many components overuse useState and how that leads to duplicated data, sync issues, and extra re-renders. It walks through deriving values from props, other state, URLs, and React Query, replacing unnecessary state with straightforward calculations. The takeaway is to store only what truly changes, derive the rest. Cleaner components, fewer bugs, and better performance.

🚅 Why a Simple Data-Structure Change Made TanStack Router 20,000× Faster
TanStack Router’s latest rewrite introduces a segment-trie–based matcher, delivering huge gains, sometimes up to 20,000× faster, as a byproduct of fixing correctness issues in the old sorted-list approach. By shifting complexity from “number of routes” to “number of URL segments,” matching no longer slows down as apps grow. The rewrite also includes optimizations like backwards stack processing, bitmasking for optional segments, typed-array parsing, and an LRU cache.

Quick Links

🍌 I Tried NotebookLM’s Nano Banana, And It Blew Past My Expectations
A space-engineering blogger shared early impressions of NotebookLM’s Nano Banana tools after testing them on his own essays. Dropping URLs or text produced polished summaries, infographics, and slide decks in minutes, far beyond what he'd normally create manually.

🤗 What They Don't Tell You About Maintaining an Open Source Project
A developer reflects on what it really takes to maintain an open-source, self-hosted project like kaneo, and how shipping v1 was only the prologue. They describe ongoing challenges with documentation, support across wildly different environments, feature requests, migrations, and contributor management. The emotional swings are real, but so are the rewards: engaged users, thoughtful PRs, and a community that makes the effort worth it.

🔀 Interactive blog posts on sorting algorithms & Computer Science
A new blog, “A Journey Through the Realms of Sorting Algorithms,” offers interactive explanations of classic and modern sorting techniques, aimed at making core computer-science concepts more intuitive. It’s especially useful for React developers or frontend engineers who want to deepen their algorithmic thinking, since the visualizations map cleanly to component state updates and render cycles. Short, approachable, and hands-on, good for brushing up on fundamentals or teaching others.

🐯 <100ms E-commerce: Instant loads with Speculation Rules API
A new post from Sentry walks through how the Speculation Rules API can make key e-commerce pages feel nearly instant by prerendering or prefetching them, especially useful for product, cart, and checkout flows. It also covers fallbacks for Safari/Firefox, how frameworks like Next.js handle prefetching, and real performance data showing large gains over “no optimization.”

🎨 Brand New Layouts with CSS Subgrid
Josh Comeau published a deep-dive on CSS Subgrid, showing how it unlocks layout patterns that were previously impossible or required awkward Flex/Grid combos. He covers fundamentals, gotchas, multi-layer subgrids, dynamic row alignment, and practical fallbacks for older browsers.