Add async functions utils.
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src/Async.tsx
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111
src/Async.tsx
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import React, {useMemo, useState} from "react";
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/**
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* Asynchronous data state.
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*/
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interface AsyncState<T>
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{
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/**
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* Determine if we are waiting for the promise result or not.
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*/
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pending: boolean;
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/**
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* The promise which is retrieved (or has retrieved) data.
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*/
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promise: Promise<T>;
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/**
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* Error thrown by the promise.
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*/
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error: Error;
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/**
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* The promise result.
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*/
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data: T;
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}
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/**
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* A promise production function.
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*/
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export type PromiseFn<T> = () => Promise<T>;
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/**
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* React hook for promise result retrieval.
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* @param promise The promise or a function that produces a promise.
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* @param deps When one of the `deps` change, it will wait for the promise again.
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*/
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export function useAsync<T>(promise: Promise<T>|PromiseFn<T>, deps: any[] = []): AsyncState<T>
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{
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// Get the actual promise from the function if there is one.
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if ((promise as PromiseFn<T>)?.call)
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promise = (promise as PromiseFn<T>)();
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else
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promise = Promise.race([promise as Promise<T>]);
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// The async state.
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const [state, setState] = useState<AsyncState<T>>({
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pending: true,
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promise: promise,
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error: undefined,
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data: undefined,
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});
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/**
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* Partial update of an async state.
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* @param stateUpdate A partial update object.
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*/
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const updateState = (stateUpdate: Partial<AsyncState<T>>) => {
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// Copy the original state and apply the partial state update.
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setState(Object.assign({}, state, stateUpdate));
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};
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// Reconfigure the promise when any deps have changed.
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useMemo(() => {
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(promise as Promise<T>).then((result) => {
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// When there is a result, disable pending state and set retrieved data, without error.
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updateState({
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pending: false,
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error: undefined,
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data: result,
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})
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}).catch((error) => {
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// An error happened, disable pending state, reset data, and set the error.
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updateState({
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pending: false,
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error: error,
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data: undefined,
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})
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});
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// Promise is ready: reset the state to pending with the configured promise, without data and error.
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updateState({
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pending: true,
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promise: promise as Promise<T>,
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error: undefined,
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data: undefined,
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});
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}, deps);
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return state; // Return the current async state.
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}
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/**
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* Wait for the promise to be fulfilled to render the children.
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* @param async The async state.
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* @param children Renderer function of the children, takes promised data as argument.
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* @param fallback Content shown when the promise is not fulfilled yet.
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* @constructor
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*/
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export function Await<T>({ async, children, fallback }: {
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async: AsyncState<T>;
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children: (async: T) => React.ReactElement;
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fallback?: React.ReactElement;
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})
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{
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// Still waiting for the promised data, showing fallback content.
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if (async.pending) return fallback ?? <></>;
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// An error happened, throwing it.
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if (async.error) throw async.error;
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// Promise is fulfilled, rendering the children with result data.
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return children(async.data);
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}
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