throttled es2015 promises

throttled-promises.js

'use strict';

var _ = require('underscore')._;

function promiseFactory (n) {
    // return () => new Promise(resolve => resolve(n));
    // return () => new Promise(resolve => setTimeout(_.partial(resolve, n), 100));
    return () => new Promise(resolve => setTimeout(_.partial(resolve, n), _.random(1000)));
}

const errorThunk = function () {
    return new Promise(() => {
        throw new Error('WRONG!');
    });
}

function throttledExecution(thunks, n) { 
    let resolveAll, rejectAll;
    let counter = 0;
    let results = _.times(thunks.length, _.noop);

    function handleResolve (index, result) {
        results[index] = _.constant(result);
        if (counter < thunks.length) {
            return executePromise();
        } else if (!_.contains(results, undefined)) {
            resolveAll(_.map(results, fn => fn()));
        }
    }

    function executePromise () {
        let index = counter++;
        const thunk = thunks[index];
        return thunk()
        .then(_.partial(handleResolve, index))
        .catch(rejectAll);
    }

    return new Promise((resolve, reject) => {
        resolveAll = resolve;
        rejectAll = reject;
        return Promise.all(_.times(_.min([n, thunks.length]), executePromise));
    });
}

let someThunks = _.times(10, promiseFactory);
throttledExecution(someThunks, 3)
.then(console.log)
.then(_.partial(throttledExecution, someThunks.concat([errorThunk]), 2))
.catch(console.log);