control-flow.js

    var results = [];

    var app = {
      initialize: function() {
        var arr = [
          this.generateMediaObj('imgs/avengers.jpg', "Avengers", "2012"),
          this.generateMediaObj('imgs/blade_runner.jpg', "Blade Runner", "1982")
        ];
        /* eachLimit(arr, limit, iterator, callback) */
        async.eachLimit(arr, 1, this.makeRequest, this.onComplete);
      },
      generateMediaObj: function(boxCover, searchName, year) {
        var mediaObj = {};
        mediaObj.boxCover = boxCover;
        mediaObj.searchName = searchName;
        mediaObj.year = year;
        mediaObj.genre = "";
        mediaObj.imdbRating = "";
        return mediaObj;
      },
      makeRequest: function(obj, callback) {
        var url = 'http://www.omdbapi.com/?t=' + obj.searchName + '&y=' + obj.year + '&plot=short&r=json';
        var request = new XMLHttpRequest();
        request.open('GET', url, true);
        request.onload = onResponse;
        request.send();

        function onResponse() {
          var response = JSON.parse(this.response);
          obj.genre = response.Genre;
          obj.imdbRating = response.imdbRating;
          results.push(obj);
          /* 
          When invoked, this callback tells async.eachLimit that this element is done with and to start with the next. 
          If there are no more elems, this.onComplete will be invoked. 
          */
          callback();
        }
      },
      /* This is called when the loop is complete and all requests have been made, results is an arr of objs */
      onComplete: function() {
        console.log(results);
      }
    };

    app.initialize();