Performance
The Next.js Page That Shipped the Database Client to the Browser
The page weighed two megabytes and the network tab showed a database driver going to the browser. A server only import crossed the boundary through one…
Error Autopsy
The Hydration Mismatch That Only Happened With an Ad Blocker
Support got screenshots of a broken header that no one could reproduce, until someone enabled an ad blocker. The client side DOM was being edited after…
Performance
The Third Party Script That Held the Main Thread Hostage
First paint waited on a vendor's deploy, because a synchronous tag manager script blocked the parser, and its long tasks queued every interaction behind…
Shopify
The Theme JavaScript That Blocked Rendering for 1.2 Seconds
One script tag without defer, loading a bundle nothing above the fold needed. How to find what is blocking your paint and what each fix actually changes.
Tooling
You Are Recording the DevTools Performance Profile Wrong
A profile recorded with a warm cache, no throttling and a mid session state measures none of the conditions your users meet, and the optimisation built on…
Deep Dive
0.1 Plus 0.2 Is Not 0.3, and Your Checkout Noticed
Currency stored as a float accumulates fractions of a cent that are invisible per transaction and visible in the reconciliation.
Performance
The Web Font That Made Your Page Invisible for Two Seconds
With font display block, the browser renders nothing where the text should be until the font arrives, and on a slow network the page is a blank skeleton…
Bug Hunt
The Request That Failed Only When the Input Contained a Comma
Search worked for every input except inputs with a comma, which 404'd. The comma is legal in a URI path, but a router in the middle split on it anyway, and…
Performance
The Endpoint That Spent Nine Hundred Milliseconds Building JSON
The query took forty milliseconds and the endpoint took nine hundred and forty. The difference was serialisation: building and stringifying forty megabytes…
Deep Dive
Node Event Loop Phases: Where Your setTimeout Really Runs
setTimeout zero and setImmediate are not the same thing, and which one runs first depends on where in the event loop you called them.
Shopify
Predictive Search Returned Nothing for a Product That Exists
The product was live, in stock and searchable from the full search page, yet the predictive suggest box returned nothing. The suggest API was not broken.
Networking
You Fixed CORS and the Browser Kept Failing for Ten Minutes
Access-Control-Max-Age caches the preflight decision, including the one that said no. Here is why your fix looked like it did not work.