chunked promise

gistfile1.js

var Promise = require('bluebird')
  , _       = require('lodash')
;


var xs = [ 1, 2, 3, 4 ];

var mapLimit = function(xs, limit, f) {
    return Promise.all(_.foldl(
          _.chunk(xs, limit)
        , function(acc, chunk) {
            return acc.then(function() {
                return Promise.all(
                    _.map(chunk, function(val) { return f(val); })
                );
            })
          }
        , new Promise(function(resolve, reject) { resolve(); })
    ));
};

mapLimit(
      xs
    , 200
    , function(val) {
        console.log("Returning promise for", val);
        return new Promise(function(resolve, reject) {
            setTimeout(function() {
                console.log("Resolved", val);
                resolve(val);
            }, 1000);
        });
      }
)
.then(function() { console.log("DONE!"); });