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Don't bother comparing constructor when deps are not provided #14594

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acdlite commented Jan 15, 2019

When no dependencies are passed to an effect hook, what we used to do is compare the effect constructor. If there was no change, then we would skip firing the effect. In practice, this is a useless optimization because the constructor will always be different when you pass an inline closure. And if you don't pass an inline closure, then you can't access any props or state.

There are some edge cases where an effect that doesn't close over props or state could be useful, like reference counting the number of mounted components. But those are rare and can be addressed by passing an empty array of dependencies.

By removing this "optimization," we can avoid retaining the constructor in the majority of cases where it's a closure that changes on every render.

I made corresponding changes to the other hooks that accept dependencies, too (useMemo, useCallback, and useImperativeHandle).

@acdlite acdlite requested a review from sebmarkbage Jan 15, 2019

@acdlite acdlite force-pushed the acdlite:never-memoize-if-no-deps branch 2 times, most recently from 8714c53 to c0d53ae Jan 15, 2019

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ReactDOM: size: 0.0%, gzip: -0.0%

Details of bundled changes.

Comparing: 71b64d5...c7d8ebc

react-dom

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nits

@acdlite acdlite force-pushed the acdlite:never-memoize-if-no-deps branch from 04cb310 to 3ef1280 Jan 17, 2019

acdlite added some commits Jan 15, 2019

Don't bother comparing constructor when deps are not provided
When no dependencies are passed to an effect hook, what we used to do is
compare the effect constructor. If there was no change, then we would
skip firing the effect. In practice, this is a useless optimization
because the constructor will always be different when you pass an inline
closure. And if you don't pass an inline closure, then you can't access
any props or state.

There are some edge cases where an effect that doesn't close over props
or state could be useful, like reference counting the number of mounted
components. But those are rare and can be addressed by passing an empty
array of dependencies.

By removing this "optimization," we can avoid retaining the constructor
in the majority of cases where it's a closure that changes on
every render.

I made corresponding changes to the other hooks that accept
dependencies, too (useMemo, useCallback, and useImperativeHandle).
Improve hook dependencies warning
It now includes the name of the hook in the message.

@acdlite acdlite force-pushed the acdlite:never-memoize-if-no-deps branch from 3ef1280 to c7d8ebc Jan 17, 2019

@acdlite acdlite merged commit 1454a8b into facebook:master Jan 17, 2019

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gaearon added a commit to gaearon/react that referenced this pull request Jan 18, 2019

gaearon added a commit that referenced this pull request Jan 18, 2019

Small tweaks to SSR to match #14594 (#14618)
* Small tweaks to SSR to match #14594

* Remove unnecessary comparison
@@ -57,6 +60,48 @@ function resolveCurrentlyRenderingComponent(): Object {
return currentlyRenderingComponent;
}

function areHookInputsEqual(

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@threepointone

threepointone Jan 18, 2019

Contributor

should this have been areHookDepsEqual?

jetoneza added a commit to jetoneza/react that referenced this pull request Jan 23, 2019

Don't bother comparing constructor when deps are not provided (facebo…
…ok#14594)

* Don't bother comparing constructor when deps are not provided

When no dependencies are passed to an effect hook, what we used to do is
compare the effect constructor. If there was no change, then we would
skip firing the effect. In practice, this is a useless optimization
because the constructor will always be different when you pass an inline
closure. And if you don't pass an inline closure, then you can't access
any props or state.

There are some edge cases where an effect that doesn't close over props
or state could be useful, like reference counting the number of mounted
components. But those are rare and can be addressed by passing an empty
array of dependencies.

By removing this "optimization," we can avoid retaining the constructor
in the majority of cases where it's a closure that changes on
every render.

I made corresponding changes to the other hooks that accept
dependencies, too (useMemo, useCallback, and useImperativeHandle).

* Improve hook dependencies warning

It now includes the name of the hook in the message.

* Nits

jetoneza added a commit to jetoneza/react that referenced this pull request Jan 23, 2019

Small tweaks to SSR to match facebook#14594 (facebook#14618)
* Small tweaks to SSR to match facebook#14594

* Remove unnecessary comparison
);
}
}
for (let i = 0; i < prevDeps.length && i < nextDeps.length; i++) {

This comment has been minimized.

@Andarist

Andarist Jan 29, 2019

Contributor

according to the previous check - those lengths should be the same, so shouldnt this iteration just assume that fact?

n8schloss added a commit to n8schloss/react that referenced this pull request Jan 31, 2019

Don't bother comparing constructor when deps are not provided (facebo…
…ok#14594)

* Don't bother comparing constructor when deps are not provided

When no dependencies are passed to an effect hook, what we used to do is
compare the effect constructor. If there was no change, then we would
skip firing the effect. In practice, this is a useless optimization
because the constructor will always be different when you pass an inline
closure. And if you don't pass an inline closure, then you can't access
any props or state.

There are some edge cases where an effect that doesn't close over props
or state could be useful, like reference counting the number of mounted
components. But those are rare and can be addressed by passing an empty
array of dependencies.

By removing this "optimization," we can avoid retaining the constructor
in the majority of cases where it's a closure that changes on
every render.

I made corresponding changes to the other hooks that accept
dependencies, too (useMemo, useCallback, and useImperativeHandle).

* Improve hook dependencies warning

It now includes the name of the hook in the message.

* Nits

n8schloss added a commit to n8schloss/react that referenced this pull request Jan 31, 2019

Small tweaks to SSR to match facebook#14594 (facebook#14618)
* Small tweaks to SSR to match facebook#14594

* Remove unnecessary comparison

@malte-wessel malte-wessel referenced this pull request Feb 2, 2019

Merged

Feature/finalize hooks #98

Kiku-git added a commit to Kiku-git/react that referenced this pull request Feb 10, 2019

Don't bother comparing constructor when deps are not provided (facebo…
…ok#14594)

* Don't bother comparing constructor when deps are not provided

When no dependencies are passed to an effect hook, what we used to do is
compare the effect constructor. If there was no change, then we would
skip firing the effect. In practice, this is a useless optimization
because the constructor will always be different when you pass an inline
closure. And if you don't pass an inline closure, then you can't access
any props or state.

There are some edge cases where an effect that doesn't close over props
or state could be useful, like reference counting the number of mounted
components. But those are rare and can be addressed by passing an empty
array of dependencies.

By removing this "optimization," we can avoid retaining the constructor
in the majority of cases where it's a closure that changes on
every render.

I made corresponding changes to the other hooks that accept
dependencies, too (useMemo, useCallback, and useImperativeHandle).

* Improve hook dependencies warning

It now includes the name of the hook in the message.

* Nits

Kiku-git added a commit to Kiku-git/react that referenced this pull request Feb 10, 2019

Small tweaks to SSR to match facebook#14594 (facebook#14618)
* Small tweaks to SSR to match facebook#14594

* Remove unnecessary comparison

andrewiggins added a commit to andrewiggins/reactjs.org that referenced this pull request Feb 12, 2019

Fix `useMemo` no dependency array description
If I understand facebook/react#14594 correctly, `useMemo` will no longer compare the given function if no dependencies are provided. This change updates the relevant sentence in the `useMemo` documentation to match the new behavior.
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