old_contents: var Article = require('../model/articles');
  var Cluster = require('../model/clusters');
  var Feed = require('../model/feeds');
  
  module.exports = (function() {
      var getCluster = function(id, promise) {
          console.log(id);
          // .populate({feed: 'feed_id', select: 'feed'})
          Cluster.findById(id).populate({path: 'articles', populate: {path: 'feed_id'}}).exec(function(err, res) {
              if (err) return handleError(err, promise);
              console.log(res);
              promise.resolve(res);
          });
      }
  
      function handleError(err, promise) {
          console.log(err);
          if (promise) promise.reject(err);
      }
  
      return {
          getCluster: getCluster
      }
  })();
  
new_contents: var Article = require('../model/articles');
  var Cluster = require('../model/clusters');
  var Feed = require('../model/feeds');
  
  module.exports = (function() {
      var getCluster = function(id, promise) {
          console.log(id);
          // .populate({feed: 'feed_id', select: 'feed'})
          Cluster.findById(id).populate({path: 'articles', populate: {path: 'feed_id'}}).exec(function(err, res) {
              if (err) return handleError(err, promise);
  
              promise.resolve(res);
          });
      }
  
      function handleError(err, promise) {
          console.log(err);
          if (promise) promise.reject(err);
      }
  
      return {
          getCluster: getCluster
      }
  })();
  
subject: Remove log