Web performance is a tricky beast, isn’t it? How do we actually know where we stand in terms of performance, and what our performance bottlenecks exactly are? Is it expensive JavaScript, slow web font delivery, heavy images, or sluggish rendering? Is it worth exploring tree-shaking, scope hoisting, code-splitting, and all the fancy loading patterns with intersection observer, server push, clients hints, HTTP/2, service workers and — oh my — edge workers? And, most importantly, where do we even start improving performance and how do we establish a performance culture long-term?
Back in the day, performance was often a mere afterthought. Often deferred till the very end of the project, it would boil down to minification, concatenation, asset optimization and potentially a few fine adjustments on the server’s config file. Looking back now, things seem to have changed quite significantly.
Performance isn’t just a technical concern: it affects everything from accessibility to usability to search engine optimization, and when baking it into the workflow, design decisions have to be informed by their performance implications. Performance has to be measured, monitored and refined continually, and the growing complexity of the web poses new challenges that make it hard to keep track of metrics, because metrics will vary significantly depending on the device, browser, protocol, network type and latency (CDNs, ISPs, caches, proxies, firewalls, load balancers and servers all play a role in performance).
So, if we created an overview of all the things we have to keep in mind when improving performance — from the very start of the process until the final release of the website — what would that list look like? Below you’ll find a (hopefully unbiased and objective) front-end performance checklist for 2020 — an updated overview of the issues you might need to consider to ensure that your response times are fast, user interaction is smooth and your sites don’t drain user’s bandwidth.
SOURCE
https://www.smashingmagazine.com/2020/01/front-end-performance-checklist-2020-pdf-pages/