Add async functions utils.

src/Async.tsx

@@ -0,0 +1,111 @@
+import React, {useMemo, useState} from "react";
+
+/**
+ * Asynchronous data state.
+ */
+interface AsyncState<T>
+{
+	/**
+	 * Determine if we are waiting for the promise result or not.
+	 */
+	pending: boolean;
+	/**
+	 * The promise which is retrieved (or has retrieved) data.
+	 */
+	promise: Promise<T>;
+	/**
+	 * Error thrown by the promise.
+	 */
+	error: Error;
+	/**
+	 * The promise result.
+	 */
+	data: T;
+}
+
+/**
+ * A promise production function.
+ */
+export type PromiseFn<T> = () => Promise<T>;
+
+/**
+ * React hook for promise result retrieval.
+ * @param promise The promise or a function that produces a promise.
+ * @param deps When one of the `deps` change, it will wait for the promise again.
+ */
+export function useAsync<T>(promise: Promise<T>|PromiseFn<T>, deps: any[] = []): AsyncState<T>
+{
+	// Get the actual promise from the function if there is one.
+	if ((promise as PromiseFn<T>)?.call)
+		promise = (promise as PromiseFn<T>)();
+	else
+		promise = Promise.race([promise as Promise<T>]);
+
+	// The async state.
+	const [state, setState] = useState<AsyncState<T>>({
+		pending: true,
+		promise: promise,
+		error: undefined,
+		data: undefined,
+	});
+
+	/**
+	 * Partial update of an async state.
+	 * @param stateUpdate A partial update object.
+	 */
+	const updateState = (stateUpdate: Partial<AsyncState<T>>) => {
+		// Copy the original state and apply the partial state update.
+		setState(Object.assign({}, state, stateUpdate));
+	};
+
+	// Reconfigure the promise when any deps have changed.
+	useMemo(() => {
+		(promise as Promise<T>).then((result) => {
+			// When there is a result, disable pending state and set retrieved data, without error.
+			updateState({
+				pending: false,
+				error: undefined,
+				data: result,
+			})
+		}).catch((error) => {
+			// An error happened, disable pending state, reset data, and set the error.
+			updateState({
+				pending: false,
+				error: error,
+				data: undefined,
+			})
+		});
+
+		// Promise is ready: reset the state to pending with the configured promise, without data and error.
+		updateState({
+			pending: true,
+			promise: promise as Promise<T>,
+			error: undefined,
+			data: undefined,
+		});
+	}, deps);
+
+	return state; // Return the current async state.
+}
+
+/**
+ * Wait for the promise to be fulfilled to render the children.
+ * @param async The async state.
+ * @param children Renderer function of the children, takes promised data as argument.
+ * @param fallback Content shown when the promise is not fulfilled yet.
+ * @constructor
+ */
+export function Await<T>({ async, children, fallback }: {
+	async: AsyncState<T>;
+	children: (async: T) => React.ReactElement;
+	fallback?: React.ReactElement;
+})
+{
+	// Still waiting for the promised data, showing fallback content.
+	if (async.pending) return fallback ?? <></>;
+	// An error happened, throwing it.
+	if (async.error) throw async.error;
+
+	// Promise is fulfilled, rendering the children with result data.
+	return children(async.data);
+}