React fiber: free-recall review
Free-recall prompts across the fiber unit. Answer each in your own words first, then reveal the model answer and compare.
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 mechanism stick.
Reconstruct the unit’s core machine — the render/commit split, the fiber double-buffer, reconciliation identity, the lane scheduler, the bailout, and tearing — without looking back at the lessons.
- 01Why can the render phase be interrupted but the commit phase cannot?
- 02What is the fiber double-buffer, and why does it make an abandoned render free?
- 03How does reconciliation reduce O(n³) tree diffing to O(n), and what role do keys play?
- 04Explain the lane model and how time-slicing keeps input responsive.
- 05What is the bailout, what gates it, and why does an inline object as a prop defeat it?
- 06What is tearing, why does only concurrent rendering expose it, and how does useSyncExternalStore prevent it?
If you could reconstruct each answer from memory, you hold the unit’s spine: render computes the diff and can be paused; commit applies it atomically; the double-buffer makes interruption free; reconciliation heuristics plus keys bind state to identity; lanes and time-slicing keep urgent input ahead of expensive work; the bailout — gated by Object.is referential stability — skips unchanged subtrees; and useSyncExternalStore keeps external stores from tearing. The reconciler is, at bottom, a machine for deciding which fibers survive an update and which are rebuilt.
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