I am learning React, especially learning useEffect.
What I can't figure out is why useEffect skips the last element of the array.
Can someone kindly explain why and how to fix it?
let users = ['Oliver', 'Thomas', 'George', 'William'] export default function App() { const [index, setIndex] = useState(0); console.log('RENDER'); useEffect(() => { if (index === users.length - 1) { return } setTimeout(() => setIndex(index => index 1), 2000) console.log('Hello ' users[index]); console.log('Side Effect RUNS!'); }, [users[index]]) } 
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Your
useEffectwill not run becauseusers[index]has the same valueChange it to
indexlet users = ['Oliver', 'Thomas', 'George', 'William'] export default function App() { const [index, setIndex] = useState(0); console.log('RENDER'); useEffect(() => { if (index === users.length - 1) { return } setTimeout(() => setIndex(index => index + 1), 2000) console.log('Hello ' + users[index]); console.log('Side Effect RUNS!'); }, [index]) // 更改为 `[index]` }