"Every bit of JavaScript you add to a site is a potential way in for a hacker. This is doubly true if that JavaScript is hosted by someone else, such as on a public CDN. Subresource Integrity is a browser feature you can use to make sure that the code being used is exactly what you intended."

"For most developers, code caching should “just work”. It works best, like any cache, when things stay unchanged, and works on heuristics which can change between versions. Nevertheless, code caching does have behaviors that can be used, and limitations which can be avoided, and careful analysis using chrome://tracing can help you tweak and optimize the use of caches by your web app."

"Our hypothesis was proven. The simpler and faster web player outperformed the old web player in all key metrics."

"ResourceTiming exposes accurate performance metrics for all of the resources fetched on your page. You can use this data for a variety of scenarios, from investigating the performance of your third-party libraries to taking specific actions when resources aren’t performing according to your performance goals."

JavaScript Loading Priorities in Chrome

Given the issues I outlined earlier, should we even consider preloading fonts?

I suspect even with Chrome’s current sub-optimal behaviour there’s a case for preloading one or maybe two critical fonts.

But don’t take my word for it, test it for yourself as your traffic mix e.g. Safari vs Chrome, the choice of server and your page make up will influence the outcome:

I tested 26 Chrome extensions to measure their impact on CPU consumption, page download size, and user experience.

Key findings:

Grammarly and Honey are super slow!
The performance impact of individual extensions is usually outweighed by the site being loaded, but they increase power consumption and having many extensions installed adds up
Extension developers can score easy wins by following best practices

tl;dr: There are no silver bullets to web performance. Simple static pages benefit from being server-rendered with minimal JavaScript. Libraries can provide great value for complex pages when used with care.

"The improvements in business and user metrics from our PWA has helped convince more people within the company of the importance of app performance and load times."

"The Server Timing header provides a discrete and convenient way to communicate backend server performance timings to developer tools in the browser. Adding timing information to your application enables you to monitor back-end and front-end performance all in one place."

"we have set up a transversal performance monitoring system that provides the basis for actions and a direct assessment of their impact. We no longer address web performance optimization as a problem but rather as a continuous improvement initiative and it perfectly fits with our culture of innovation and excellence."

Measuring Web Performance for Wikipedia using synthetic testing tools

Preload Best Practice: Only use preload="auto" if there is a high probability that the video will be watched. In general, the use of preload="metadata" provides a good balance in data usage vs. startup time, but should be monitored for excessive data usage.

"This extensive review shows how little we really know about performance perception and how inadequate the metrics currently used as industry standards probably are"