performance

Bundling combines multiple JavaScript modules into optimized files for production, while code splitting breaks them apart strategically so users only download what they need for the current page.

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.

Images typically account for 50%+ of a page's total weight, making format selection, responsive sizing, lazy loading, and compression the highest-impact performance wins for most websites.

Lazy loading defers the loading of non-critical resources until they are needed, reducing initial page weight and improving Time to Interactive through native attributes, Intersection Observer, and dynamic imports.

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.

Core Web Vitals are Google's three key metrics (LCP, INP, CLS) that measure real-world user experience for loading speed, interactivity, and visual stability, directly impacting search rankings.

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.

Debouncing delays execution until a pause in activity while throttling limits execution to fixed intervals, and choosing the right technique for each use case is a frequent interview question and essential for responsive UIs.

React performance optimization involves preventing unnecessary re-renders with memoization, virtualizing long lists, splitting context providers, and profiling with React DevTools to identify actual bottlenecks before optimizing.

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.