Slowness loading pages with new esbuild

[paolodamico]

In what situation are you experiencing subpar performance?

App navigation now feels noticeably slower when loading new pages for the first time. One time it even took more than 6s, and because there's no loader, it feels like something is broken. A recording that doesn't look too drastic:

How to reproduce

See recording above.

Environment

• PostHog Cloud

Additional context

Originally posted on https://github.com/PostHog/product-internal/issues/220. Moving here.

Thank you for your performance issue report – we want PostHog to go supersonic!

[paolodamico]

Context from @Twixes:

Regarding the slowness, that doesn't seem related to the new UI. Maybe it's esbuild chunking? Looks like esbuild first downloads the initial page chunk, and only then determines what others chunks to load, leading to a staggered load (totaling ~1 second of wait time on first scene load).

[paolodamico]

From @mariusandra:

Hmm, this behaviour is not optimal. It can be solved though.
We can use esbuild's build metadata to determine which urls need which chunks, and then have index.html load all of them directly. Just more work to do, but doable.