text: const mongoose = require('mongoose')
  
  const DB_URL = 'mongodb://localhost:27017/test'
  
  mongoose.connect(DB_URL)
  
  mongoose.connection.on('connected',function() {
     console.log('Mongoose connection open to '+DB_URL);
  });
  /**
  * 连接异常 error 数据库连接错误
  */
  mongoose.connection.on('error',function(err) {
    console.log('Mongoose connection error: '+ err);
  });
  /**
  * 连接断开 disconnected 连接异常断开
  */
  mongoose.connection.on('disconnected',function() {
    console.log('Mongoose connection disconnected');
  });
  
  module.exports = mongoose