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import type { AnyFunction } from '../types'
/**
* Runs a check to determine if the given result function behaves as an
* identity function. An identity function is one that returns its
* input unchanged, for example, `x => x`. This check helps ensure
* efficient memoization and prevent unnecessary re-renders by encouraging
* proper use of transformation logic in result functions and
* extraction logic in input selectors.
*
* @param resultFunc - The result function to be checked.
* @param inputSelectorsResults - The results of the input selectors.
* @param outputSelectorResult - The result of the output selector.
*
* @see {@link https://reselect.js.org/api/development-only-stability-checks#identityfunctioncheck `identityFunctionCheck`}
*
* @since 5.0.0
* @internal
*/
export const runIdentityFunctionCheck = (
resultFunc: AnyFunction,
inputSelectorsResults: unknown[],
outputSelectorResult: unknown
) => {
if (
inputSelectorsResults.length === 1 &&
inputSelectorsResults[0] === outputSelectorResult
) {
let isInputSameAsOutput = false
try {
const emptyObject = {}
if (resultFunc(emptyObject) === emptyObject) isInputSameAsOutput = true
} catch {
// Do nothing
}
if (isInputSameAsOutput) {
let stack: string | undefined = undefined
try {
throw new Error()
} catch (e) {
// eslint-disable-next-line @typescript-eslint/no-extra-semi, no-extra-semi
;({ stack } = e as Error)
}
console.warn(
'The result function returned its own inputs without modification. e.g' +
'\n`createSelector([state => state.todos], todos => todos)`' +
'\nThis could lead to inefficient memoization and unnecessary re-renders.' +
'\nEnsure transformation logic is in the result function, and extraction logic is in the input selectors.',
{ stack }
)
}
}
}
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