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// Before: only React events were batched.
setTimeout(() => {
setCount(c => c + 1);
setFlag(f => !f);
// React will render twice, once for each state update (no batching)
}, 1000);
// After: updates inside of timeouts, promises,
// native event handlers or any other event are batched.
setTimeout(() => {
setCount(c => c + 1);
setFlag(f => !f);
// React will only re-render once at the end (that's batching!)
}, 1000);