Bug: useReducer runs the queued updates with new props

[a-c-sreedhar-reddy]

React version: 16.8.0

Steps To Reproduce

Link to code example:
https://codesandbox.io/s/usereducer-wfcmq Link to codesandbox.

The current behavior

Initially step is 0. So for every step react does not rerender due to this https://github.com/facebook/react/blob/master/packages/react-reconciler/src/ReactFiberHooks.js#L1347. But state updates are queued. So when step changes all the state updates are done and hence creates a bug by adding the new step prop.

https://overreacted.io/a-complete-guide-to-useeffect/#why-usereducer-is-the-cheat-mode-of-hooks

[vkurchatkin]

I’m not 100% sure, but I think that reducer is supposed to be pure, i.e. you can’t use props, otherwise no guarantees are provided

[a-c-sreedhar-reddy]

I think since prop is a constant, won't reducer be pure?

[markerikson]

My understanding is that this is both a result of how the reducer function is being defined and capturing local values, and actually entirely intentional behavior.

[a-c-sreedhar-reddy]

But if the prop is changed then previous actions which are queued but not applied since they were giving the same state are being applied on the new reducer.

[markerikson]

As I said, per Dan's post, this appears to be intentional, and not a bug.

[gaearon]

Is this the same problem as #15088 (comment)?

[a-c-sreedhar-reddy]

yeah @gaearon. Is it a bug or feature?

[gaearon]

I think it's a bug.

[a-c-sreedhar-reddy]

Why are the updates queued when it is known that no state has been changed?

[gaearon]

Because it is a bug?

[stale]

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