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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 | |
| } | |