SOURCE

function sleep(delay) {
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            resolve(delay)
        }, delay);
    })
}

Promiseall = function(promises, max) {
    let curLen = 0;
    let maxLen = max;
    let queue = [];
    let pLen = promises.length;
    let complete = 0;
    let results = new Array(pLen);
    return new Promise((resolve, reject) => {
        function run() {
            while (curLen < maxLen && queue.length) {
                const {promise, i} = queue.shift();
                curLen++;
                promise.then((value) => {
                    console.log(value);
                    results[i] = value;
                    complete++;
                    curLen--;
                    if (complete === pLen) {
                        resolve(results);
                    }
                    run();
                }).catch((error) => {
                    reject(error);
                });

            }
        }
        promises.forEach((promise, i) => {
            queue.push({promise, i});
            run();
        })
    })
}

const promises = [sleep(2000), sleep(1000), sleep(4000), sleep(3000)];
Promiseall(promises, 2).then((results) => {
    console.log(results);
})