Everything that's actually inside a sourcemap and how it can quietly expose your codebase, TanStack Router maintainer Nicolas Beaussart on migrating 1.5 million lines without stopping the team, and a big batch of community reads, grouped by topic this time.
New article: Everything you need to know about Sourcemaps
A production error at bundle.min.js:1:48211 tells you absolutely nothing. Sourcemaps are the thing that turns it back into a real file, line, and variable name.
I wrote an article explaining almost everything about sourcemaps. It starts with what's actually in the JSON — sources, names, mappings, sourcesContent — then follows the transformation there and back, looks at who can fetch your .map files in production, and how to keep the debugging benefits without publishing your codebase along the way.
Read the full article here
Podcast: Nicolas Beaussart on routing at scale
New episode of Señors @ Scale is out. Nicolas Beaussart-Hatchuel is a Staff Engineer at PayFit and a maintainer of TanStack Router.
We went through the full story of migrating a 1.5 million-line codebase from React Router v5 to TanStack Router using the strangler pattern with 18 engineers still shipping 15-20 PRs a day while two routers ran side by side on the same URL.
Also we talk about how PayFit killed micro frontends entirely and consolidated 25 repos into a single monorepo, and building the whole app at once saved 25MB of JavaScript.
Watch the full episode on YouTube
Listen on Spotify
Community reads
A longer list than usual, so I grouped them by topic.
Design and CSS
Building glass for the web by Aave Labs — Apple's liquid-glass look rebuilt for every modern browser with SVG displacement maps, and the components refract the live DOM, not a screenshot of it.
The best loading states are no loading states by Jenna Smith — fewer spinners and skeletons scattered through components, more route transitions and preloading.
CSS can now animate between pages by David Krcek — cross-document view transitions with a single @view-transition rule, no JavaScript and no SPA router required.
Falling in love with the build by Karl Koch — designer-engineers have no handoff checkpoint to challenge them, so they build the delightful thing first and justify it afterwards. His recommendation: write the reasoning down before writing the code.
AI and agents
The great agent skills land grab by Den Odell — most agent "skills" published on GitHub repackage knowledge the models already have; the valuable ones encode things the agent couldn't get on its own.
Agent security considerations for WebMCP by Chrome for Developers — the two main attack vectors when AI agents use WebMCP, and the guardrails worth layering against prompt injection.
How to make your design system AI-ready by Vitaly Friedman — treating design decisions as infrastructure, with specification files, token layers, and auditing scripts, so the AI never has to interpret your visual patterns on its own.
Loop engineering by Addy Osmani — the shift from prompting coding agents by hand to designing loops where agents prompt themselves until they hit the goal.
Claude Fable 5 and Claude Mythos 5 by Anthropic — the new model family: Fable 5 for everyone, Mythos 5 gated to approved cybersecurity professionals, with safety classifiers routing the most sensitive requests.
Web platform
News from WWDC26: WebKit in Safari 27 beta by the WebKit team — 58 new features and 525 fixes, including customizable <select> elements, scroll anchoring, and the :heading pseudo-class.
Streaming HTML by Ollie Williams — streaming a fetch response straight into the DOM.
Web accessibility ROI by David Gibson — a study of 10,000 sites where the WCAG-compliant ones gained 23% more organic traffic and ranked for 27% more keywords.
Engineering and tooling
How TypeScript infers type variables by Nicolas Laurent — the two-phase algorithm behind generic inference, and the rules for unions, intersections, and conditionals.
TanStack Table V9: taking form by Kevin Van Cott — the next major version moves state onto TanStack Store with granular re-rendering, tree-shakable features, and lower memory use on large virtualized tables.
SQLite: improving performance with pre-sort by Anders Murphy — pre-sorting batches before inserting them is 2-3x faster, because B+ trees hate random keys.
Stop using conventional commits by Sumner Evans — the case that type-first commit prefixes get the hierarchy backwards, and that scope-first messages, the way Linux and Go do it, deliver what conventional commits only promises.
That's it for this one.
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