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inconsistent behavior with undefined value #807

tvolodimir opened this issue Jun 3, 2021 · 2 comments

inconsistent behavior with undefined value #807

tvolodimir opened this issue Jun 3, 2021 · 2 comments


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@tvolodimir tvolodimir commented Jun 3, 2021

馃悰 Bug Report

Starting from 8.0.2, was changed 'produce' behavior with assigning 'undefined' value. And now it looks not consistent.

Link to repro

To Reproduce

// const immer = require('immer@8.0.1');
const immer = require('immer@9.0.2');

const state = {};
const newState = immer.produce(state, draft => {
    draft.baz = undefined;

// output: 
// @9.0.2: false 
// @8.0.1: false
console.log(state === newState); 

// output: 
// @9.0.2: {}
// @8.0.1: {baz: undefined}

Observed behavior

Behavior at 8.0.1 looks normal as I am changed state from {} to {baz: undefined} and of course, it's a new object.
But at 8.0.2-9.0.2 I see no change from state {} to {} but somehow get a new object, that is cause incomprehension and also cause problems at existing code

Expected behavior

First of all how to properly handle this in 8.0.2-9.0.2.

const newState = immer.produce(state, draft => {
  if (draft.baz !=== undefined) { // should I have to add checks before each assigning ?
      draft.baz = undefined;

Or there are possibility to force produce to add fields with 'undefined' values?


  • Immer version:
  • I filed this report against the 9.0.2 version of Immer
  • Occurs with setUseProxies(true)
@mweststrate mweststrate added the bug label Jun 9, 2021
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@mweststrate mweststrate commented Jun 9, 2021

Thanks for reporting, looks like a regression indeed!

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@github-actions github-actions bot commented Jul 5, 2021

馃帀 This issue has been resolved in version 9.0.4 馃帀

The release is available on:

Your semantic-release bot 馃摝馃殌

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