Promise.all in short

promise.all.ts

// inline type declaration for ES6 Promise object
// see full at https://github.com/DefinitelyTyped/DefinitelyTyped/blob/master/es6-promise/es6-promise.d.ts
declare class Promise {
    constructor(callback: (resolve: (value?: any) => void, reject: (reason?: any) => void) => void);
    then(onFulfilled?: (any) => any, onRejected?: (any) => any|void);
}

const isPromise: (p:any) => boolean = p => typeof p === 'object' && typeof p.then === 'function';

const promiseAll: (promises:any[]) => Promise = promises => new Promise((resolve, reject) => {
    let results = [],
        pendingCount = promises.length,
        _resolve = (result, index) => {
            results[index] = result;
            if (--pendingCount === 0) {
                console.log(`All resolved: ${results}`);
                resolve(results);
            }
        };
    promises.forEach((promise, index) => {
        /*if (!isPromise(promise)) {
            console.log(`value at ${index} is not a promise, resolve to ${promise}`);
            _resolve(promise, index);
        } else {
            promise.then(result => {
                console.log(`promise ${index} resolved to ${result}`);
                _resolve(result, index);
            }, reject);
        }*/
        // with Promise.resolve, this can be simple as:
        Promise.resolve(promise).then(result => _resolve(result, index), reject);
    });
});

// test
let promises:any[] = [
    0,
    new Promise(resolve => setTimeout(() => resolve(1), 2000)),
    new Promise(resolve => setTimeout(() => resolve(2), 1500))
];

promiseAll(promises).then(results => console.log(results));