Add concept of StrictMode levels 1 & 2 (no public API yet) by bvaughn · Pull Request #20844 · react/react

bvaughn · 2021-02-18T21:28:20Z

PR Stack

Add concept of StrictMode levels 1 & 2 (no public API yet) #20844: Add concept of StrictMode levels 1 & 2 (no public API yet)
Separate strict effects mode feature flags #20847: Separate strict effects mode feature flags
Add StrictMode level prop and createRoot unstable_strictModeLevel option #20849: Add StrictMode level prop and createRoot unstable_strictModeLevel option

Strict mode level 0 (aka loose or sloppy mode)

This isn't really a mode so much as it's the absence of any strict modes.

Strict mode level 1 (aka legacy mode)

The exported <React.StrictMode> tag remains the same and opts legacy subtrees into strict mode level one (mode == StrictLegacyMode). This mode enables DEV-only double rendering, double component lifecycles, string ref warnings, legacy context warnings, etc. The primary purpose of this mode is to help detected render phase side effects. No new behavior. Roots created with experimental createRoot and createBlockingRoot APIs will also (for now) continue to default to strict mode level 1.

Strict mode level 2 (aka strict effects mode)

In a subsequent commit I will add support for a "level" attribute on the <React.StrictMode> tag (as well as a new option supported by createRoot). This will be the way to opt into strict mode level 2 (mode == StrictEffectsMode). This mode will enable DEV-only double invoking of effects on initial mount (see #19523). This will simulate future Offscreen API semantics for trees being mounted, then hidden, and then shown again. The primary purpose of this mode is to enable applications to prepare for compatibility with the new Offscreen API (more information to follow shortly).

Strict mode level >= 3?

In the future we may add additional strict mode levels (TBD).

External changes?

For now, this commit changes no public facing behavior. The only mechanism for opting into strict mode level 2 is the pre-existing enableDoubleInvokingEffects feature flag (only enabled within Facebook for now).

sizebot · 2021-02-18T21:43:52Z

Comparing: 4190a34...372bb8b

Critical size changes

Includes critical production bundles, as well as any change greater than 2%:

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
oss-stable/react-dom/cjs/react-dom.production.min.js	=	122.36 kB	122.36 kB	=	39.41 kB	39.41 kB
oss-experimental/react-dom/cjs/react-dom.production.min.js	=	128.94 kB	128.94 kB	=	41.47 kB	41.47 kB
facebook-www/ReactDOM-prod.classic.js	+0.06%	404.67 kB	404.90 kB	+0.07%	75.15 kB	75.20 kB
facebook-www/ReactDOM-prod.modern.js	+0.06%	393.02 kB	393.24 kB	+0.08%	73.24 kB	73.30 kB
facebook-www/ReactDOMForked-prod.classic.js	+0.06%	404.68 kB	404.91 kB	+0.07%	75.15 kB	75.20 kB

Significant size changes

Includes any change greater than 0.2%:

Expand to show

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
oss-experimental/react-debug-tools/cjs/react-debug-tools.development.js	+0.48%	21.31 kB	21.41 kB	+0.89%	5.84 kB	5.89 kB
oss-stable/react-debug-tools/cjs/react-debug-tools.development.js	+0.48%	21.31 kB	21.41 kB	+0.89%	5.84 kB	5.89 kB

Generated by 🚫 dangerJS against 372bb8b

dai-shi · 2021-02-18T22:34:02Z

StrictMode level sounds nice.
I hope it would be possible to add useRef read warning on mutable values, at some level.
#18545 (comment)

bvaughn · 2021-02-18T22:35:27Z

Both of the new warnings you refer to are related to render phase side effects, so if anything they both belong in level 1. An argument could be made for warning about mutated refs even outside of strict mode.

jacobp100 · 2021-02-19T10:05:41Z

Sorry if this is too off-topic - does this mean double invoking the functions passed to useEffect?

eps1lon · 2021-02-19T10:26:59Z

Sorry if this is too off-topic - does this mean double invoking the functions passed to useEffect?

@jacobp100 For what "strict effects mode" is, check out the original PR:

TL;DR: It doesn't just double invoke the functions passed to useEffect (create) but also runs their cleanup logic inbetween:

This PR changes the behavior in DEV when an effect runs from create() to create() -> destroy() -> create()

--#19523

bvaughn · 2021-02-19T18:44:45Z

Circle CI doing something weird here I think. Hm. Should sort itself out next time I rebase onto master.

rickhanlonii

I still wonder if we can wait on this until we have more information but happy to move forward if others want to approve and land.

rickhanlonii

Looks great, these changes are really exciting 🎉

rickhanlonii · 2021-02-24T19:08:50Z

 import {emptyRefsObject} from './ReactFiberClassComponent.new';
 import {isCompatibleFamilyForHotReloading} from './ReactFiberHotReloading.new';
-import {StrictMode} from './ReactTypeOfMode';
+import {StrictLegacyMode} from './ReactTypeOfMode';


Chatted offline and we can follow up with this if we agree - we may want to name this something other than "legacy" since the term overloaded to mean "legacy root", "legacy strict mode" and any other "legacys" we have. I was thinking something like:

NoMode = 0

StrictWarningMode = Level 1

StrictRenderMode = Level 2

StrictEffectMode = Level 3

…y subtrees into strict mode level one ('mode == StrictModeL1'). This mode enables DEV-only double rendering, double component lifecycles, string ref warnings, legacy context warnings, etc. The primary purpose of this mode is to help detected render phase side effects. No new behavior. Roots created with experimental 'createRoot' and 'createBlockingRoot' APIs will also (for now) continue to default to strict mode level 1. In a subsequent commit I will add support for a 'level' attribute on the '<React.StrictMode>' tag (as well as a new option supported by ). This will be the way to opt into strict mode level 2 ('mode == StrictModeL2'). This mode will enable DEV-only double invoking of effects on initial mount. This will simulate future Offscreen API semantics for trees being mounted, then hidden, and then shown again. The primary purpose of this mode is to enable applications to prepare for compatibility with the new Offscreen API (more information to follow shortly). For now, this commit changes no public facing behavior. The only mechanism for opting into strict mode level 2 is the pre-existing 'enableDoubleInvokingEffects' feature flag (only enabled within Facebook for now).

StrictModeL1 -> StrictLegacyMode and StrictModeL2 -> StrictEffectsMode

bvaughn · 2021-02-24T21:14:36Z

Merged via #20849

bvaughn requested review from acdlite, gaearon, rickhanlonii and sebmarkbage February 18, 2021 21:28

facebook-github-bot added CLA Signed React Core Team Opened by a member of the React Core Team labels Feb 18, 2021

bvaughn force-pushed the strict-mode-level-1-and-2 branch from e12cf07 to f0a5fac Compare February 18, 2021 21:30

acdlite reviewed Feb 18, 2021

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Comment thread packages/react-reconciler/src/ReactTypeOfMode.js Outdated

bvaughn mentioned this pull request Feb 19, 2021

Separate strict effects mode feature flags #20847

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bvaughn changed the title ~~Add StrictMode levels 1 & 2~~ Add concept of StrictMode levels 1 & 2 (no public API yet) Feb 19, 2021

bvaughn force-pushed the strict-mode-level-1-and-2 branch from e52ca35 to dd40e13 Compare February 19, 2021 16:33

bvaughn mentioned this pull request Feb 19, 2021

Add StrictMode level prop and createRoot unstable_strictModeLevel option #20849

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rickhanlonii reviewed Feb 19, 2021

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bvaughn force-pushed the strict-mode-level-1-and-2 branch from dd40e13 to 11b8797 Compare February 22, 2021 20:09

bvaughn requested review from acdlite and rickhanlonii February 23, 2021 14:51

rickhanlonii approved these changes Feb 24, 2021

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Brian Vaughn added 2 commits February 24, 2021 14:54

Renamed strict mode constants

372bb8b

StrictModeL1 -> StrictLegacyMode and StrictModeL2 -> StrictEffectsMode

bvaughn force-pushed the strict-mode-level-1-and-2 branch from 11b8797 to 372bb8b Compare February 24, 2021 20:24

bvaughn closed this Feb 24, 2021

bvaughn deleted the strict-mode-level-1-and-2 branch February 24, 2021 21:14

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Add concept of StrictMode levels 1 & 2 (no public API yet)#20844

Add concept of StrictMode levels 1 & 2 (no public API yet)#20844
bvaughn wants to merge 2 commits into
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PR Stack

Strict mode level 0 (aka loose or sloppy mode)

Strict mode level 1 (aka legacy mode)

Strict mode level 2 (aka strict effects mode)

Strict mode level >= 3?

External changes?

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