Break up long tasks and minimize hydration so the page responds quickly to clicks and taps.
INP replaced FID as a Core Web Vital in 2024 (target < 200ms). Long main-thread tasks delay every interaction.
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Interaction to Next Paint measures responsiveness across the page's lifetime; the target is < 200ms. Long tasks (> 50ms) block input handling, so chunk heavy work and ship less JS to hydrate.
// bad: one long synchronous task blocks input
items.forEach(process); // 400ms task
// good: yield to the main thread between chunks
for (const item of items) {
process(item);
if (navigator.scheduling?.isInputPending()) await scheduler.yield?.();
}Defer non-critical work, debounce handlers, and prefer server components / partial hydration to shrink the JS that must run on load.