mongoose连接数据库出错

今天学习mongodb的时候连接数据库半天都没连上，代码如下

const mongoose = require('mongoose');

mongoose.connect('mongodb://localhost:27017/juejin')

mongoose.connection.on('open',()=>{
    console.log('连接成功')
})

mongoose.connection.on('close',()=>{
    console.log("断开连结")
})
 mongoose.connection.on('error',(err)=>{
    console.log("连接失败")
 })

去mongoose官网看了半天，复制了他的一段代码就连接成功了，把localhost改成127.0.0.1就能连接上了

const mongoose = require('mongoose');

mongoose.connect('mongodb://127.0.0.1:27017/juejin')

mongoose.connection.on('open',()=>{
    console.log('连接成功')
})

mongoose.connection.on('close',()=>{
    console.log("断开连结")
})
 mongoose.connection.on('error',(err)=>{
    console.log("连接失败")
 })