javascript-解决mongoose数据查询的异步操作

//原来的代码
var shoppingModel = global.dbHandle.getModel('shopping');
var cartsshop = [];
for(var i = 0;i<carts.length;i++){
shoppingModel.findOne({title:carts[i].title},function (err,shops) {
  if(err){
    return next(err);
  }else{
    cartsshop.push(shops);
  }
 });
}
console.log(cartsshop);//[]

//event.js 文件
var EventEmitter = require('events').EventEmitter; 
var event = new EventEmitter(); 
event.on('some_event', function() { 
  console.log('some_event 事件触发'); 
}); 
setTimeout(function() { 
  event.emit('some_event'); 
}, 1000); 

var shoppingModel = global.dbHandle.getModel('shopping');
var cartsshop = [];
var obj ;
var j = 0;
var myEventEmitter = new events.EventEmitter();
myEventEmitter.on('next',addResult);
function addResult() {
  cartsshop.push(obj);
  j++;
  if(j==carts.length){
    console.log(cartsshop);
    res.json(cartsshop);
  }
}
for(var i = 0;i<carts.length;i++){
  var ii = i;
 shoppingModel.findOne({title:carts[ii].title},function (err,shops) {
  if(err){
    return next(err);
  }else{
    obj = shops;
    myEventEmitter.emit('next');
  }
 });
}

var events = require('events');