LoAF - Andy Davies - performance.now() 2025

Over time the web has become more reliant on JavaScript. Some believe JavaScript is the only way to build the modern web and dismiss the performance concerns, while others hold opposing views. Wouldn't it be great if we had data on how scripts actually perform in our visitor's browsers – when they delay loading, cause jankiness and slowdown interactions, and perhaps more importantly which scripts are responsible? After all, if we can't measure it, how can we improve it? The Long Tasks API was a first attempt at providing this data but it couldn't answer the question of why the main thread was busy. The Long Animation Frames (LoAF) API aims to overcome the weaknesses by also providing details on what Main Thread activity caused the long frame, if possible. Slides: https://noti.st/andydavies/9JOItx/making-sense-of-loaf *** A session from performance.now(), the web performance conference. Each November in Amsterdam; see https://perfnow.nl for more information. Conference announcements in your inbox? https://perfnow.nl/subscribe