Network waterfall

Each button fetches the same small file 30 times, with a cache-busting parameter so every request is real. Open DevTools → Network and tick Disable cache before you start.

Watch the shape of the waterfall, not the total. Sequential stair-steps. The pool is five waves of six. Promise.all depends on the protocol: over HTTP/2 it is one solid block, but over HTTP/1.1 the browser opens six connections and queues the rest, so it looks almost like the pool. The log shows which protocol each run used.

1 · Sequential 2 · Promise.all 3 · Pool of 6 Clear log