#Web Performance
Images Fail on Mobile in Pages Hidden with display:none
A site switches pages using display:none, but opening another page on mobile leaves blank black images, even though the files return 200 and both fetch and new Image succeed. The culprit is the IntersectionObserver behind loading=lazy not firing when the page changes from none to block, and simply setting loading=eager is still not enough.
Site Not Updating After Deploy — Clear All Five Cache Layers
The files are uploaded, but the site still shows the old version, even after Ctrl+F5 — because five cache layers sit between the files on disk and what people see, and each needs a different clearing method. This article covers the sequence I use regularly, along with the trap that leaves the site stuck on 500 after clearing the view cache.
Moving Computation from PHP to the Browser: 12 Seconds to 12 ms
A single page ran tens of thousands of subqueries and took 12 seconds to load. I fixed it by precomputing a summary table, sending a single 107 KB dataset, and moving the formulas to the browser, bringing computation down to 12 milliseconds, with a parity test that requires JS results to match PHP on every row.