Gemini · OpenAI
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Why the reconciler batches updates
State updates are queued and flushed together, so several calls in one handler produce a single render pass.
Where effects actually run
- Layout effects fire before the browser paints.
- Passive effects are deferred until after paint.
- Cleanup runs before the next effect, not after unmount only.
Quotes
You are not fighting the renderer. You are fighting your own assumptions about when it runs.
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How rendering actually works
A walk through the render, commit, and paint phases — and the mental model that makes the rest of the API stop feeling arbitrary.
Key points
- 01Rendering is a pure function of props and state.
- 02Committing is the only phase that touches the DOM.
- 03Keys tell the reconciler what identity means.
- 04Memoization is a cache, not a correctness fix.
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What happens when you call setState twice in one handler?
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Did they say anything about error boundaries?
Yes — around the middle of the video. The point made was that error boundaries only catch errors during rendering, lifecycle methods, and constructors.
They explicitly do not catch errors inside event handlers, async code, or on the server.