@reactivex/ix-esnext-esm/asynciterable/forkjoin.js

import { identity, identityAsync } from '../internal/identity';
// tslint:disable-next-line:no-empty
const NEVER_PROMISE = new Promise(() => { });
function wrapPromiseWithIndex(promise, index) {
    return promise.then(value => ({ value, index }));
}
export async function forkJoin(...sources) {
    let fn = sources.shift();
    if (typeof fn !== 'function') {
        sources.unshift(fn);
        fn = identityAsync;
    }
    const length = sources.length;
    const iterators = new Array(length);
    const nexts = new Array(length);
    let active = length;
    const values = new Array(length);
    const hasValues = new Array(length);
    hasValues.fill(false);
    for (let i = 0; i < length; i++) {
        const iterator = sources[i][Symbol.asyncIterator]();
        iterators[i] = iterator;
        nexts[i] = wrapPromiseWithIndex(iterator.next(), i);
    }
    while (active > 0) {
        const next = Promise.race(nexts);
        const { value: next$, index } = await next;
        if (next$.done) {
            nexts[index] = NEVER_PROMISE;
            active--;
        }
        else {
            const iterator$ = iterators[index];
            nexts[index] = wrapPromiseWithIndex(iterator$.next(), index);
            hasValues[index] = true;
            values[index] = next$.value;
        }
    }
    if (hasValues.every(identity)) {
        return await fn(values);
    }
    return undefined;
}

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