Engineering case
Listing prices in dollars
A small personal tool: the extension prints a dollar figure next to every rouble price using the central bank rate, and a bot watches for new listings matching saved searches.
Two independent detectors find the price so that a markup change does not break the tool: a walk over text nodes climbing a few ancestors, and a fallback guess by class names. Cards loaded while scrolling are caught by a mutation observer, and redrawing waits for the browser to go idle.
Watching listings needs no headless browser: the page is fetched with a plain request and the data is read from the application state the page already ships in its markup.
Manifest V3 · JavaScript · Node.js · SQLite · Telegram Bot API