Deep dive into React's internal reconciliation engine rewrite.
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01
Understand the problem
fiberarchitecturereconciliation
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02
Attempt it yourself
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03
03
Study the solution
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04
Read the code
Concurrent priority with useTransition
import { useState, useTransition } from "react";
export default function App() {
const [text, setText] = useState("");
const [list, setList] = useState([]);
const [isPending, startTransition] = useTransition();
const onChange = (e) => {
setText(e.target.value); // urgent: keep input responsive
startTransition(() => { // non-urgent: Fiber can interrupt
setList(Array.from({ length: 5000 }, (_, i) => e.target.value + " " + i));
});
};
return (
<div style={{ padding: 24, fontFamily: "system-ui" }}>
<input value={text} onChange={onChange} placeholder="type fast" />
{isPending && <span> updating…</span>}
<p>{list.length} rows</p>
</div>
);
}05
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