useState wouldn't work asynchronously (array)

user_9315566 0
Viewed 28

I would like to reflect state asynchronously. But when I add a value, it is not reflected asynchronously. How can I solve this problem?

const [values, setValues] = useState<string[]>([])
const [input, setInputs] = useState<string>()

const add = useCallback(() => {
  if(!input) return
  values.push(input)
  setValues(values)
}, [input, values])

...
<input onChange={() => setInput(e.target.value) />
<button onClick={() => add()}>Add</button>

// not displayed asynchrnously
{values && values.map((value, idx) => {
  return (
    <div key={idx}>{value}</div>         
  )
})}
...
reactjs
1 Answers

When setting the existing state based on the previous state, the recommended way to do it is to send a callback function to the state setting function.

I have modified your add function to reflect this:

const add = useCallback(() => {
  if (input) {
    setValues(prev => [...prev, input])
  }
}, [input, setValues])

Also, your callback function for setting the input was missing the event parameter and had a typo. I have fixed both issues:

<input onChange={e => setInput(e.target.value)} />
user_3375540
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