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import { useCallback, useReducer, useRef } from 'react'
/**
* Create a selector that updates when an `update` function is called, and
* which only causes the component to render when the result of `selector`
* differs from the previous result according to `equalityFn`.
*
* If `selector` is memoized using `useCallback`, then it will only be called
* when it changes or when `update` is called. Otherwise, `selector` will be
* called every time the component renders.
*
* @example
* const [state, update] = useGenericSelector(selector, equalityFn)
*
* useIsomorphicLayoutEffect(() => {
* return addEventListener(update)
* }, [addEventListener, update])
*
* return state
*/
export function useGenericSelector<T>(
selector: () => T,
equalityFn: (a: T | null, b: T) => boolean
): [state: T, update: () => void] {
const [, forceRender] = useReducer(s => s + 1, 0)
const latestSubscriptionCallbackError = useRef<Error | undefined>()
const latestSelector = useRef<() => T>(() => null as any)
const latestSelectedState = useRef<T | null>(null)
let selectedState: T
try {
if (
selector !== latestSelector.current ||
latestSubscriptionCallbackError.current
) {
const selectorResult = selector()
if (equalityFn(latestSelectedState.current, selectorResult)) {
selectedState = latestSelectedState.current as T
} else {
selectedState = selectorResult
}
} else {
selectedState = latestSelectedState.current as T
}
} catch (err) {
if (latestSubscriptionCallbackError.current && isError(err)) {
err.message += `\nThe error may be correlated with this previous error:\n${latestSubscriptionCallbackError.current.stack}\n\n`
}
throw err
}
latestSelector.current = selector
latestSelectedState.current = selectedState
latestSubscriptionCallbackError.current = undefined
const update = useCallback(() => {
try {
const newSelectedState = latestSelector.current()
if (equalityFn(latestSelectedState.current, newSelectedState)) {
return
}
latestSelectedState.current = newSelectedState
} catch (err) {
// we ignore all errors here, since when the component
// is re-rendered, the selectors are called again, and
// will throw again, if neither props nor store state
// changed
if (err instanceof Error) {
latestSubscriptionCallbackError.current = err
} else {
latestSubscriptionCallbackError.current = new Error(String(err))
}
}
forceRender()
// don't rerender on equalityFn change since we want to be able to define it inline
// eslint-disable-next-line react-hooks/exhaustive-deps
}, [])
return [selectedState, update]
}
function isError(error: any): error is Error {
return error instanceof Error
}
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