text: const mongoose = require('mongoose');
  const Schema = mongoose.Schema;
  mongoose.connect('mongodb://localhost/chatroom');
  const userSchema = new Schema({
      nickname: {
          type: String,
          required: true
      },
      password: {
          type: String,
          required: true
      },
      salt: {
          type: String,
          required: true
      },
      avatar: {
          type: String,
          required: true
      }
  });
  module.exports = mongoose.model('User', userSchema);