Request waterfall

Requests that wait for each other in sequence when they could run in parallel, so load time adds up.

A typical case: the page loads, then a component fetches the user, then a child fetches the user’s projects, then another child fetches details. Each step waits for the previous one, and on a slow mobile network four round trips can take longer than everything else on the page. The name comes from the staircase shape in the browser’s network panel.

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Related terms

Core Web Vitals (LCP, INP, CLS): Google’s three metrics of real user experience: loading (LCP), responsiveness (INP) and visual stability (CLS).
React Server Components (RSC): React components that run only on the server, send rendered output instead of JavaScript, and can read data directly.
Event loop: How JavaScript runs one task at a time and queues the rest: callbacks, promises (microtasks), timers and rendering.

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