通过连接字符串从node.js连接到MongoDB数据库（官方推荐）

var MongoClient = require('mongodb').MongoClient;
MongoClient.connect('mongodb://dbuser:dbpassword@localhost/dbname', {
 db: {
 w: 1,
 native_parser: false
 },
 server: {
 poolSize: 5,
 socketOptions: {connectTimeoutMS: 500},
 auto_reconnect: true
 },
 replSet: {},
 mongos: {}
}, function(err, db) {
 if (err) {
 console.log('失败');
 }else {
 console.log('成功');
 db.logout(function(err, result) {
 if (!err) {
 console.log('成功断开数据库连接');
 }
 db.close();
 console.log('数据库连接关闭！');
 });
 }
});