Asynchronous loop issues illustrative example

gistfile1.js

// Illustrative case
// YEAH -- ILLUSTRATIVE OF THE FACT THAT YOU CAN ISSUE PARALLEL QUERIES TO THE DATABASE INSTEAD OF SERIAL ONES LIKE A DUMB THREADED IMPLEMENTATION THAT IS INFERIOR FOR DOING WEB SERVERS

function (recentBlogPostIds, callback) { // obviously you need this, but use callback instead of return

  var results = [], // Use array not object
    , len = recentBlogPostIds.length; // Cache length since we'll be using it more than once
    
  for (var i = 0; i < len; i++) {
    var blogPostId = recentBlogPostIds[i];
    // var results = []; <-- RESETTING results IN THE FOR LOOP IS WRONG EVEN WITHOUT ASYNC!

    function(i) { // use self-executing anonymous function to scope iteration variable
      // Fetch from DB
      asynchronousDB.getBlogPostById(blogPostId, function(err, blogPostId, post) {
        results[blogPostId] = post;
        if (i === len - 1) callback(results);
      });
    }(i)

  }

  // Return results
  // return results; <-- WRONG, THE I/O HASN'T HAPPENED YET

}