Function reiterable

Extension/src/Utility/Async/iterators.ts:37–68

(iterable: AsyncIterable<T>)

/** An AsyncIterable wrapper that caches so that it can be iterated multiple times */
export function reiterable<T>(iterable: AsyncIterable<T>): AsyncIterable<T> {
    const cache = new Array<T>();
    let done: boolean | undefined;
    let nextElement: undefined | Promise<IteratorResult<T>>;

    return {
        [Symbol.asyncIterator]() {
            let index = 0;
            return {
                async next() {
                    if (index < cache.length) {
                        return { value: cache[index++], done: false };
                    }
                    if (done) {
                        return { value: undefined, done: true };
                    }
                    index++;
                    if (!is.promise(nextElement)) {
                        nextElement = iterable[Symbol.asyncIterator]().next().then(element => {
                            if (!(done = element.done)) {
                                cache.push(element.value);
                            }
                            nextElement = undefined;
                            return element;
                        });
                    }
                    return nextElement;
                }
            };
        }
    };
}

export type AsynchIterable<T> = AsyncIterable<T> & {
    add(...iterables: (Some<T> | undefined | Promise<T> | Promise<undefined | T>)[]): void;