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ReactIntermediate#routing
ReactIntermediate#state
Why should you not mutate state directly?
React compares references to decide what changed, so mutating an object or array in place can skip the re-render entirely and makes bugs hard to trace. Always produce a new value.
Example
// wrong
items.push(x); setItems(items);
// right
setItems([...items, x]);
setUser(u => ({ ...u, name: 'New' }));