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Object not extensible when referencing old recoil value in callback

See original GitHub issue

In a callback, I am granular-ly updating a property of a Recoil state object.

I’m doing something similar to

const [toUpdate, setToUpdate] = useRecoilState(someAtom) 
socket.on("this_event", (data: any) => {
    setToUpdate((toUpdate: any) => {


        return toUpdate

or the syntax

setToUpdate((toUpdate: any) => {

    const newToUpdate = Object.assign({},toUpdate)

    return newToUpdate


both throw an “object not extensible” error. This sytnax works fine in vanilla React state and was wondering if this is a bug or if there’s a workaround to setting a property of a Recoil state?

I’ve been able to get a temporary workaround by doing

setToUpdate((toUpdate: any) => {

    const newToUpdate = JSON.parse(JSON.stringify(toUpdate))

    return newToUpdate


since it completely copies the contents, but it is very hacky and in the long term very slow

Issue Analytics

  • State:closed
  • Created 3 years ago
  • Comments:15 (5 by maintainers)

github_iconTop GitHub Comments

drarmstrcommented, Jun 10, 2020

@quuu - Objects stored in Recoil state are frozen by default. We want to ensure that we are capturing all “state changes” to properly update other nodes in the data-flow graph or React components which depend on that state. However, in some cases it may make sense to override this, which you can do so with the dangerouslyAllowMutability option in the atom or selector.

pnkflydgrcommented, Jul 28, 2020

Just for thoroughness I want to share what I found is a better approach than JSON.parse() for deep cloning.

import { cloneDeep } from "lodash"
const [stateObj, setStateObj] = useRecoilState(objAtom)
const nestedChangeHandler = ((...) => {
  let clonedStateObj = cloneDeep(stateObj)
  // update nested properties of clonedStateObj

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