Question 1

How do I read the Performance panel without getting lost?

Accepted Answer

Start with the flame chart (timeline of JS/CSS/paint). Look for long red blocks (layout thrashing), yellow (rendering), green (scripting). Use the "Main" track to find bottlenecks. Record for 5-10 seconds, zoom to the slow part, identify the culprit function in the call tree. FCP (First Contentful Paint) and LCP (Largest Contentful Paint) are the metrics that matter for UX.

Question 2

How do I debug memory leaks in production?

Accepted Answer

Memory panel → Take heap snapshots at app start and after user actions. Compare snapshots (detached DOM nodes = leak signal). Look for growing retainer chains. Most common: event listeners never cleaned up, timers never cleared, circular refs. Use the Allocation Timeline to record leaks over time. Fix by cleaning up in component unmount/teardown.

Question 3

What's Network throttling and when do I use it?

Accepted Answer

Emulate slow networks (3G/4G) to test real-world UX. DevTools → Network tab → throttle preset. Slow 3G = common in emerging markets; you'll find loading-state bugs and lazy-load issues fast. Test on a real phone too, DevTools mobile emulation is close but not exact (no real radio, no real thermal).

Question 4

Should I set up Lighthouse CI in my pipeline?

Accepted Answer

Yes. Lighthouse CI (via npm package) runs in CI, fails the build if performance < threshold (e.g. LCP > 2.5s or CLS > 0.1). Catches regressions before they ship. Configure thresholds per route (homepage stricter than admin). Takes 30s per build.

Question 5

How do I profile JavaScript with the right tool?

Accepted Answer

Performance panel → click 'Record' → let it run 5-10s → stop. Main track shows function call tree + time. Look for long tasks (>50ms) that block the main thread. For continuous profiling, use the JS Profiler panel (not Flame Chart) to see aggregated time per function. DevTools shows call stacks that let you drill from slow function → its parent → the trigger.

Question 6

How do I emulate mobile without buying a phone?

Accepted Answer

DevTools → Devices → iPhone 15 / Android. Emulates touch, viewport, pixel ratio, user agent. Great for layout testing. NOT exact: no real network latency, no real GPU, no real CPU throttle. Always test on real hardware for performance-critical features. Use Network throttling (Slow 3G) + CPU throttling (4x slowdown) together to approximate real mobile.

Question 7

Is AI available in DevTools yet?

Accepted Answer

Yes (Chrome 127+). DevTools → Help → panel shows 'Ask DevTools AI' in Styles/Console for explanations. Uses Gemini (requires opt-in). Useful for 'why does this selector not match?' or 'what does this error mean?' Not magic; still needs human judgment. Off by default; enable in Settings → Experiments.

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