[breaking change] implement and default to useStrictShallowCopy, omitting getters

[hrsh7th]

Description

Fixes #867

This PR improves the performance when updating the object that contains a large number of entries.

Problem

The current immer takes a long time for creating new object when the draft object has large amount of keys.

From some of the investigation, I found the cause that is getOwnPropertyDescriptors (here) .

In my computer, the ownKeys and its iteration don't take a long time but getOwnPropertyDescriptors takes time near the 10ms.

I can understand that the getOwnPropertyDescriptors is needed. Because immer should copy object's descriptors such as getter/setter/non-enumerable keys.

But some of the users doesn't need that strictness, I think.

Solution

Add the ability to opt-out of strict shallow copy implementation for performance reasons.

edited

Make the default behavior not strict shallow copy. And add the ability to opt-in to strict shallow copying.

import { useStrictShallowCopy } from 'immer';

useStrictShallowCopy(true); // opt-in strict shallow copy.

Result

The following results show the benefit of this patch.

// Iteration count:
//   50
//
// Base object: 
//   Array(10000)
//   	.fill(0)
//   	.map((_, i) => [i, i])
// 
// Test case:
//   for (let i = 0; i < MAX; i++) {
//   	produce(baseState, draft => {
//   		draft[5000]++
//   	})
//   }

# large-obj - mutate large object

immer (proxy) - with setUseStrictShallowCopy: 354ms
immer (proxy) - without setUseStrictShallowCopy: 79ms
immer (es5) - with setUseStrictShallowCopy: 1228ms
immer (es5) - without setUseStrictShallowCopy: 655ms

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[mweststrate]

I didn't read the code yet, but could you include a rationale in the PR description, what are you updating and why is it faster, what does the API look like, in which cases will it break things, etc?

[coveralls]

Pull Request Test Coverage Report for Build 4024919453

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• 18 of 19 (94.74%) changed or added relevant lines in 5 files are covered.
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• Overall coverage decreased (-0.1%) to 98.168%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/core/immerClass.ts	3	4	75.0%

Totals
Change from base Build 3932225358:	-0.1%
Covered Lines:	801
Relevant Lines:	813

---

💛 - Coveralls

[hrsh7th]

Thank you for your advice.
I will update the PR description and try a more rational explanation.
It may take some time.

[gregdingle]

@hrsh7th @mweststrate this looks like a great PR to give users (like me) meaningfully better performance with large objects (>1000 keys).

Was it closed just for lack of activity?

[mweststrate]

It was missing rationale IIRC when it was closed, but now I see it is present, so reopening :) It might take some time to process though due to my own personal circumstances. Apologies upfront!

[mweststrate]

I think it makes sense to make this behavior the new default, ship it as separate major version and make the old behavior opt-in using a flag.

[hrsh7th]

Thank you for your review.

Nice to hear that this PR is an acceptable change.

I noticed that the test is failing. I will fix it.

[hrsh7th]

Could you approve the GitHub Actions?

In my environment, this branch is passed the all tests... I want to re-try GitHub Actions.

[mweststrate]

done!

[hrsh7th]

Thank you! It seems to pass the tests.
I'll do the necessary work, such as fixes that change the default behavior.

[hrsh7th]

This test is ugly, but after some consideration, I think it should be the spec.

First, I thought that non-enumerable properties should not be visible from drafts when useStrictShallowCopy is false.

However, achieving this behavior requires checking whether the referenced property is non-enumerable, which introduces new overhead.

[hrsh7th]

I'm not confident about the documentation part, but I think the code part is ready for review.

[github-actions]

🎉 This PR is included in version 10.0.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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