Browser & Frontend Runtime
Core Web Vitals: free-recall review
Retrieval beats re-reading. For each prompt, say or write a full answer from memory before you open the model answer — the effort of recall is what makes the material stick.
Reconstruct the unit’s spine — what each vital measures and its threshold, the LCP phase split, the INP parts and the hydration trap, CLS scoring, the field-vs-lab rule, and the shared-budget discipline — without looking back at the lessons.
- 01What does each Core Web Vital measure, what is its 'good' threshold, and where are they measured?
- 02Name the four LCP phases and the fix for each, and explain why you must read the split before applying a fix.
- 03Name the three parts of INP, and explain the early-only INP pattern and what it points to.
- 04How is one CLS shift scored, what is the session window, and what does the 500 ms exclusion do?
- 05Explain the lab-vs-field distinction and give the rule for when to use each.
- 06Why must you measure all three vitals before and after any change, and what does complete production observability require?
If you reconstructed each answer from memory, you hold the unit’s spine: LCP/INP/CLS are field metrics at p75 with thresholds ≤2.5 s, ≤200 ms, ≤0.1; LCP is read by its four phases and INP by its three parts so you fix the dominant one; the early-only INP pattern is the hydration signature; CLS is impact × distance over the worst 5 s window with a 500 ms post-interaction exclusion; the verdict lives in the field (CrUX), the lab is for debugging and CI; and because all three share a budget, every change is measured against all of them with RUM plus a CI gate.