Meta node: I find this presentation style to be great. You can scroll up and down at speed, can text search the whole page, we have a nice mixture of imagery and text, its clean and accessible, we even have a table of contents. How did you author this?
HTTP2 is a doddle to implement. Do it.
PWA makes it possible to work fully offline.
With CSS best to chuck it all out including those reset files someone wrote a decade ago. Instead re-write the whole lot using CSS Grid and using custom variables.
Inline the SVG into the CSS as custom variables.
Get rid of the bulk of the JS by only targeting evergreen browsers. No polyfills, no jQueries, just minimal javascript that does a lot of things in the PWA and manipulates CSS custom variables rather than the DOM.
Use HTML5 properly, with no lip service. Get rid of JS for forms and rely on HTML5 to do it.
Pagespeed to sort out the images and make them into source sets.
The goal of a lot of the above is to strip out convoluted build tools and have actual neat HTML that can be maintained. No more 'add only' CSS to hand on to the next guy, instead have something with comments in the code and sensible names that target HTML5 things like 'main' and 'aside' or 'nav' rather than made up class names.
A final thought is that the starting point can be to build a green website, i.e. one that cause too much cruft to be downloaded. This is the same thing as 'minimizing/cutting out bloat' but I find that setting out to build a website that sets the example of being green is a better mindset than 'must do those hacky things to make website faster'.
I also found them useful recently for small (28x28px) thumbnail images on my personal website. On average, saved as a PNG the thumbnails were 20kb, as a JPEG 9kb, and as an optimized GIF about 1-2kb. With about 100 thumbnails on one of the pages, the savings are pretty significant. (At least, this seemed to be the best approach; if anyone with more knowledge of image compression has a better suggestion, please let me know).
Also, there doesn't seem to be anything on JSON minification, which is a sizable portion of responses. There are techniques to transpose JSON objects to be easier to gzip compress.
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