Promise.props

Promise.props(Object|Map|Promise<Object|Map> input) -> Promise

Like .all but for object properties or Maps* entries instead of iterated values. Returns a promise that is fulfilled when all the properties of the object or the Map's' values** are fulfilled. The promise's fulfillment value is an object or a Map with fulfillment values at respective keys to the original object or a Map. If any promise in the object or Map rejects, the returned promise is rejected with the rejection reason.

If object is a trusted Promise, then it will be treated as a promise for object rather than for its properties. All other objects (except Maps) are treated for their properties as is returned by Object.keys - the object's own enumerable properties.

*Only the native ECMAScript 6 Map implementation that is provided by the environment as is is supported

**If the map's keys happen to be Promises, they are not awaited for and the resulting Map will still have those same Promise instances as keys

Promise.props({
    pictures: getPictures(),
    comments: getComments(),
    tweets: getTweets()
}).then(function(result) {
    console.log(result.tweets, result.pictures, result.comments);
});

var Promise = require("bluebird");
var fs = Promise.promisifyAll(require("fs"));
var _ = require("lodash");
var path = require("path");
var util = require("util");

function directorySizeInfo(root) {
    var counts = {dirs: 0, files: 0};
    var stats = (function reader(root) {
        return fs.readdirAsync(root).map(function(fileName) {
            var filePath = path.join(root, fileName);
            return fs.statAsync(filePath).then(function(stat) {
                stat.filePath = filePath;
                if (stat.isDirectory()) {
                    counts.dirs++;
                    return reader(filePath)
                }
                counts.files++;
                return stat;
            });
        }).then(_.flatten);
    })(root).then(_.chain);

    var smallest = stats.call("min", "size").call("pick", "size", "filePath").call("value");
    var largest = stats.call("max", "size").call("pick", "size", "filePath").call("value");
    var totalSize = stats.call("pluck", "size").call("reduce", function(a, b) {
        return a + b;
    }, 0);

    return Promise.props({
        counts: counts,
        smallest: smallest,
        largest: largest,
        totalSize: totalSize
    });
}


directorySizeInfo(process.argv[2] || ".").then(function(sizeInfo) {
    console.log(util.format("                                                \n\
        %d directories, %d files                                             \n\
        Total size: %d bytes                                                 \n\
        Smallest file: %s with %d bytes                                      \n\
        Largest file: %s with %d bytes                                       \n\
    ", sizeInfo.counts.dirs, sizeInfo.counts.files, sizeInfo.totalSize,
        sizeInfo.smallest.filePath, sizeInfo.smallest.size,
        sizeInfo.largest.filePath, sizeInfo.largest.size));
});

Note that if you have no use for the result object other than retrieving the properties, it is more convenient to use Promise.join:

Promise.join(getPictures(), getComments(), getTweets(),
    function(pictures, comments, tweets) {
    console.log(pictures, comments, tweets);
});