(Until YouTube allows replacing videos, audio issues are fixed at https://vimeo.com/300240534) Everyone loves fast sites. While "make your site faster" is a simple mantra, the actual steps to achieve this can be daunting. Fortunately, we know where to start: JavaScript. JavaScript consumes twice as much CPU as loading, layout, and rendering combined. Byte-for-byte, JavaScript inflicts more delays on sites than any other resource, and yet the amount of JavaScript on sites continues to grow. In this session you'll learn the latest techniques for measuring and improving the impact JavaScript on your site, including: using the User Timing Spec and Long Tasks API to track the CPU cost of JavaScript for real users, moving expensive JavaScript off the main thread, using code coverage tools to reduce your JavaScript, and understanding why defer is probably a better technique than async for loading JavaScript. Slides: https://www.slideshare.net/souders/make-javascript-faster About Steve: https://stevesouders.com/ More about performance.now(); https://perfnow.nl or https://twitter.com/perfnowconf Receive conference announcements in your inbox: https://perfnow.nl/subscribe