Moved a Core Web Vitals collection setup designed for shared observability infrastructure to my personal blog. Fixed a dashboard left empty by sparse traffic and changed when metrics are collected for ordinary browsers. This post records the changes from October 17 to 22, query omissions investigated on October 23, and what five days of data can support.
Sent the Core Web Vitals measured in an app webview to an observability platform shared by many teams. The webview gave no signal on leaving, and tail sampling, delta-to-cumulative conversion and Tempo queries each dropped values in their own way without raising an error. For every setting that could not be changed, re-measured what was lost in a reproduction environment.
Traced why CLS and INP go missing when the page is left, through the transport of OTel JS and the order in which flush runs.
Checked the conditions under which web-vitals 6.2.3 reports each metric, and why INP goes missing when the page is left right after a click.
Tracing a coldpath misclassification that read every synchronous dependency in the Turbopack analysis file as a static import. This post compares the graph information and build output of webpack, Turbopack, Vite, and esbuild, and looks at which clues reveal the original syntax and which cases cannot be recovered.
Next.js 16's cacheComponents hides the pages you leave with React Activity instead of unmounting them. Following a three.js canvas that went blank after a back navigation, I read the router, React, and react-three-fiber source and reproduced it in a browser.
Chuseok side quest, part 3: with love, to Toss Securities
Chuseok side quest, part 2: building a V8 coverage analyzer, one dead end after another.
Chuseok side quest, part 1: starting with my own blog
I imported one constant and 97.7% of the bundle came along with it. The vendor had no timeline for a fix, so I pried open the published source maps, recovered over 400 TypeScript files, and rewrote the build, the entry points, and the dependencies however I wanted. Everything except the logic. That got /send to -77.5% raw. The hard part came after. All 1,932 tests passed, and a few of them were watching nothing at all.
I set out to confirm the 500 ms hint that part 2 left behind, but the hard reloads that would form the control group arrive at under one a day. So I built the control group myself, with Playwright and a shaping proxy, and found that going through the worker costs 2 ms on a navigation, and that the cost is not latency but the bytes the worker fetches in the background on every click. The gap I had left between the lab and the field turned out, only after the post was written, to be a measurement definition difference created by 103 Early Hints. Third part of the service worker caching deep dive series.
In a Next.js 16 Turbopack production build, a module-scope singleton became two live instances at runtime. Inside the same synchronous block, one condition contradicted the other, and responses that arrived in 30ms still timed out. This is the record of tracing the cause through the bundle output: a partial scope hoisting merge, a circular import, an upstream bug that had already been fixed, and the single-variable experiment I ran too late.
A banner built with framer-motion made the entire home screen stutter for the 0.6 seconds it took to open. The record of guessing the cause from the code, having that guess overturned twice by measurement, and finally removing the reflow with a single easing function. Plus what the work left behind: the gap between declaration and execution, the principle that properties decide performance, preserving mechanisms, suspecting your instruments first, and proving sameness with a curve.
I dropped typescript 7.0.2 into a monorepo where pnpm lint took 12 minutes 32 seconds. Type checking passed quietly, but next build broke and lint crashed. A record of the chain reaction from one day of swapping eslint and prettier for oxlint and oxfmt, with before-and-after measurements. To say it up front, the build did not get any faster.
Even a deploy that changes not a single line of code leaks errors. This is a measured record of tagging every failure that leaks during rolling deploys by type and timestamp, performing an autopsy on four causes, and stacking prescriptions one layer at a time until the count reaches zero. Includes the actual Next.js shutdown code, hostage draining, and the real CrashLoopBackOff timetable. Part 4 of the Kubernetes for frontend developers series.
A Service's ClusterIP is an IP attached to no machine, yet curl reaches it. iptables rules and conntrack, EndpointSlice, cluster DNS and ndots, Gateway, and port-forward: a record of opening up the entire path a request takes to a pod, directly in a kind cluster. Part 3 of the Kubernetes for frontend developers series.
A look at V8's generational garbage collection, adjusting heap memory limits, and practical ways to diagnose memory leaks.
Why try...catch misses errors thrown in async functions, and how to handle every case: IIFEs, forEach, promise chains, constructors, event listeners, and global safety nets.
Why GitHub Actions scheduled workflows get delayed by dozens of minutes: the structural causes, and free alternatives that actually run on time.
