text: var MongoClient = require('mongodb').MongoClient;
  var assert = require('assert');
  var url = 'mongodb://localhost:27017/zk';
  
  var show = (db, callback) => {
    var cursor = db.collection('mycol').find();
    cursor.each((err, doc) => {
      assert.equal(err, null);
      if(doc !== null){
        callback(doc);
      }
    })
  };
  
  
  MongoClient.connect(url, function(err, db){
    assert.equal(null, err);
  
    console.log('Connected correctly to server.');
  
    show(db, (doc) => {
      console.dir(doc);
      db.close();
    });
  
  });
  