parallelTask

index.js

module.exports = async function parallelTask(task, shouldEnd, max) {
    let i = 0;
    let runningCnt = 0;
    return new Promise((resolve, reject) => {
        function check() {
            if (shouldEnd(i)) {
                return;
            }
            if (runningCnt > max) {
                return;
            }
            const promise = task(i);
            i++;
            runningCnt++;
            promise.then(() => {
                runningCnt--;
                check();
                if (runningCnt === 0) {
                    resolve();
                }
            }).catch(function (e) {
                reject(e);
            })
            check();
        }
        check();
    });

}

index.ts

module.exports = async function parallelTask<T>(
    task: (index: number) => Promise<T>,
    shouldEnd: (index: number) => boolean,
    max: number
): Promise<T[]> {
    let i = 0;
    let runningCnt = 0;
    return new Promise((resolve, reject) => {
        const ret: T[] = [];
        function check() {
            if (shouldEnd(i)) {
                return;
            }
            if (runningCnt > max) {
                return;
            }
            const promise = task(i);
            const index = i;
            i++;
            runningCnt++;
            promise
                .then(result => {
                    ret[index] = result;
                    runningCnt--;
                    check();
                    if (runningCnt === 0) {
                        resolve(ret);
                    }
                })
                .catch(function (e) {
                    reject(e);
                });
            check();
        }
        check();
    });
};