Cheat Sheet
| Question | Core Idea | Senior Signal |
|---|---|---|
| Q221 | Main thread | Find what blocks input to next paint, then reduce urgent work or split non-urgent work. |
| Q222 | Workers | Use workers for CPU-bound work with typed messages, stale-result handling, and transfer-cost awareness. |
| Q223 | Memory | Leaks are unwanted retained references; debug with heap snapshots and retaining paths. |
| Q224-Q225 | Rendering and capstone | Classify style, layout, paint, memory, JS, React, worker, or vendor cost before fixing. |