performance

Web caching stores previously fetched resources at various layers (browser, CDN, service worker) to reduce network requests, lower latency, and enable offline access in production applications.

Memory leaks occur when JavaScript retains references to objects that are no longer needed, causing steadily increasing memory consumption that degrades performance and can eventually crash the browser tab.

Production performance monitoring combines synthetic testing (Lighthouse CI) with Real User Monitoring (RUM) to track metrics over time, enforce performance budgets, and alert teams when regressions occur.

Choosing between CSR, SSR, SSG, and ISR determines when and where HTML is generated, while understanding the Critical Rendering Path (DOM, CSSOM, render tree, layout, paint) reveals how browsers turn that HTML into visible pixels.

Runtime performance focuses on what happens after the page loads: identifying long tasks that block the main thread, avoiding layout thrashing, using requestAnimationFrame for smooth animations, and offloading heavy computation to Web Workers.