MongoDB 使用 Node.js 获取集合中的文档数量（计数）

我目前正在编写一个函数，该函数应该返回集合中的文档数量，问题是当我返回值时它显示未定义，这是我的代码：

    var MongoClient = require('mongodb').MongoClient;


// open the connection the DB server
var dbName = "ystocks";
var port = "27017";
var host = "localhost";
var tt = "mongodb://" + host + ":" + port + "/" + dbName;
//"mongodb://localhost:27017/ystocks"
function getNumOfDocs (collectionName, host, port, dbName) {
    var tt = "mongodb://" + host + ":" + port + "/" + dbName;
    count = 0;
    MongoClient.connect(tt, function (error, db){

        if(error) throw error;
        collectionName = collectionName;
        db.collection(collectionName).count({}, function(error, numOfDocs){
            if (error) throw error;

            //print the result
            console.dir("numOfDocs: " + numOfDocs);
            count = numOfDocs;
            console.log("count is : " + count);

            // close the DB
            return numOfDocs;
            db.close();


        });// end of count

    }); // Connection to the DB
    //return count;

} // end of getNumOfDocs


var ee = getNumOfDocs ("stocks", "localhost", "27017", "ystocks");
console.log("ee is " + ee);

请帮我。

这是如何做到的should看起来像

var MongoClient = require('mongodb').MongoClient;

var dbName = "ystocks";
var port = "27017";
var host = "localhost";

function getNumOfDocs (collectionName, host, port, dbName, callback) {
    MongoClient.connect("mongodb://" + host + ":" + port + "/" + dbName, function (error, db){
        if(error) return callback(error);

        db.collection(collectionName).count({}, function(error, numOfDocs){
            if(error) return callback(error);

            db.close();
            callback(null, numOfDocs);
        });
    }); 
} 

及用法

getNumOfDocs("stocks", host, port, dbName, function(err, count) {
   if (err) {
       return console.log(err.message);
   }
   console.log('number of documents', count);
});

请记住，如果您要多次调用此函数，最好只连接到数据库一次，然后使用相同的连接。