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Data: Include more details when shallow equality fails in 'useSelect' #67713

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merged 3 commits into from
Dec 9, 2024
Merged

Data: Include more details when shallow equality fails in 'useSelect' #67713

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9f92c5e
Data: Include more details when shallow equality fails in 'useSelect'
Mamaduka Dec 8, 2024
39bc8c1
Simplify keys logic
Mamaduka Dec 9, 2024
b53a3a3
Update early return condition
Mamaduka Dec 9, 2024
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22 changes: 18 additions & 4 deletions packages/data/src/components/use-select/index.js
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,23 @@ import useAsyncMode from '../async-mode-provider/use-async-mode';

const renderQueue = createQueue();

function warnOnUnstableReference( a, b ) {
let keys = [];
if ( a.constructor === Object && b.constructor === Object ) {
keys = Object.keys( a ).filter( ( k ) => a[ k ] !== b[ k ] );
} else if ( Array.isArray( a ) && Array.isArray( b ) ) {
keys = [ ...a.keys() ].filter( ( i ) => a[ i ] !== b[ i ] );
}
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Object.keys should work equally well also for arrays. The only difference is that .keys() returns numbers, while Object.keys are strings.

The a.constructor check will crash when a is null or undefined, we should guard for that.

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Object.keys should work equally well also for arrays. The only difference is that .keys() returns numbers, while Object.keys are strings.

Yeah. I should have guessed that 😅

The a.constructor check will crash when a is null or undefined, we should guard for that.

I've borrowed the check for isShallowEqual, so it should be safe in this case.

Based on your suggestion, I think we can simplify logic to the example below. What do you think?

const keys =
	typeof a === 'object' && typeof b === 'object'
		? Object.keys( a ).filter( ( k ) => a[ k ] !== b[ k ] )
		: [];

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I've borrowed the check for isShallowEqual, so it should be safe in this case.

But isShallowEqual does an if ( a && b ) check before it starts looking at a.constructor.

typeof a === 'object' && typeof b === 'object'

typeof null is also 'object' 🙀 It will all work only if you exit early when a or b is falsy.

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I should stop ignoring the "everything is an object" JS motto 😄

Pushed update in 39bc8c1.


// eslint-disable-next-line no-console
console.warn(
'The `useSelect` hook returns different values when called with the same state and parameters.\n' +
'This can lead to unnecessary re-renders and performance issues if not fixed.\n\n' +
'Non-equal value keys: %s\n\n',
keys.join( ', ' )
);
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The warning will be confusing when the b object has some field that the a object doesn't have. Then it will report an empty list of non-equal keys.

It can happen in practice when we write code like this:

useSelect( select => {
  if ( someCondition ) {
    return { loading: false };
  }
  return { loading: false, data: select( store ).getData() };
} );

To fix this, we could construct a set of all fields on both objects and then filter it:

const allKeys = Array.from( new Set( [ ...Object.keys( a ), ...Object.keys( b ) ] ) );
const keys = allKeys.filter( ( k ) => a[ k ] !== b[ k ] );

But this will fail again for objects like {} and { a: undefined } which are not shallow equal but keys will be [].

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The warning will be confusing when the b object has some field that the a object doesn't have. Then it will report an empty list of non-equal keys.

It means that the b run happened with different state or parameters (mostly params, based on your example). That shouldn't be the case for this warning, as it only makes sense with the same state/params.

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Oh that's true, I've been overthinking it 🙂 Running the mapSelect callback twice with the same state shouldn't produce objects like this unless you're doing it on purpose.

}

/**
* @typedef {import('../../types').StoreDescriptor<C>} StoreDescriptor
* @template {import('../../types').AnyConfig} C
Expand Down Expand Up @@ -159,10 +176,7 @@ function Store( registry, suspense ) {
if ( ! didWarnUnstableReference ) {
const secondMapResult = mapSelect( select, registry );
if ( ! isShallowEqual( mapResult, secondMapResult ) ) {
// eslint-disable-next-line no-console
console.warn(
`The 'useSelect' hook returns different values when called with the same state and parameters. This can lead to unnecessary rerenders.`
);
warnOnUnstableReference( mapResult, secondMapResult );
didWarnUnstableReference = true;
}
}
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