Custom useFieldArray hook for formik using immutability-helper

useFieldArray.js

import {useCallback, useRef, useEffect} from 'react'
import {useField, useFormikContext} from 'formik'
import update from 'immutability-helper'

const useFieldArray = props => {
  const [field, meta] = useField(props)
  const fieldArray = useRef(field.value)
  const {setFieldValue} = useFormikContext()

  useEffect(() => {
    fieldArray.current = field.value
  }, [field.value])

  const push = useCallback(value => {
    fieldArray.current = update(fieldArray.current, {
      $push: [value]
    })

    setFieldValue(field.name, fieldArray.current)
  }, [field.name, setFieldValue])

  const swap = useCallback((indexA, indexB) => {
    const swapA = fieldArray.current[indexA]
    const swapB = fieldArray.current[indexB]

    fieldArray.current = update(fieldArray.current, {
      $splice: [[indexA, 1, swapB], [indexB, 1, swapA]]
    })

    setFieldValue(field.name, fieldArray.current)
  }, [field.name, setFieldValue])

  const move = useCallback((from, to) => {
    const toMove = fieldArray.current[from]

    fieldArray.current = update(fieldArray.current, {
      $splice: [[from, 1], [to, 0, toMove]]
    })

    setFieldValue(field.name, fieldArray.current)
  }, [field.name, setFieldValue])

  const insert = useCallback((index, value) => {
    fieldArray.current = update(fieldArray.current, {
      $splice: [[index, 0, value]]
    })

    setFieldValue(field.name, fieldArray.current)
  }, [field.name, setFieldValue])

  const unshift = useCallback(value => {
    fieldArray.current = update(fieldArray.current, {
      $unshift: [value]
    })

    setFieldValue(field.name, fieldArray.current)
    return fieldArray.current.length
  }, [field.name, setFieldValue])

  const remove = useCallback(index => {
    const removedItem = fieldArray.current[index]

    fieldArray.current = update(fieldArray.current, {
      $splice: [[index, 1]]
    })

    setFieldValue(field.name, fieldArray.current)
    return removedItem
  }, [field.name, setFieldValue])

  const pop = useCallback(() => {
    const lastIndex = fieldArray.current.length - 1
    const poppedItem = fieldArray.current[lastIndex]

    fieldArray.current = update(fieldArray.current, {
      $splice: [[lastIndex, 1]]
    })

    setFieldValue(field.name, fieldArray.current)
    return poppedItem
  }, [field.name, setFieldValue])

  const replace = useCallback((index, value) => {
    fieldArray.current = update(fieldArray.current, {
      $splice: [[index, 1, value]]
    })

    setFieldValue(field.name, fieldArray.current)
  }, [field.name, setFieldValue])

  return [
    field,
    meta,
    {
      push,
      swap,
      move,
      insert,
      unshift,
      remove,
      pop,
      replace
    }
  ]
}

export {useFieldArray}

There was a sync issue bug but throwing a useEffect in there (lines 10-12) to keep the ref in sync with field.value seems to fix it. Hopefully doesn't cause other weird issues 😅

Oh that must be what was causing my issue today. Ill add that and see if I can remove my addition

  const reset = useCallback(
    (v) => {
      fieldArray.current = v
      setFieldValue(field.name, fieldArray.current)
    },
    [field.name, setFieldValue]
  )

Plus I exported the helpers from useField

how to update this to useFastArrayHelper, in order to update local state?

@thadeu Not 100% sure what you mean, but guessing you want to return the helpers from useField? If so you should just be able to change line 6 to const [field, meta, helpers] = useField(props) and then just add helpers to the returned array. I haven't tried using those methods with this hook personally, but it should just work I think.

Can you use it in an example? I keep getting: "update(): expected target of $push to be an array; got undefined."

@Bulletninja here is the "friend list" example taken from the formik docs and modified to work with useFieldArray: https://codesandbox.io/s/eloquent-leakey-v70t1?file=/src/App.js

Thanks a lot!

I was having weird sync issues again recently (not sure what changed 🤔)

Haven't looked into it too closely, but as a quick fix changing from useEffect to useLayoutEffect seems to work. It can delay the rendering if you are pushing in lots of items, but at least no data gets lost...

We need this as a part of formik.