Model user.js

const mongoose = require('mongoose');
const bcrypt = require('bcrypt');

const userSchema = new mongoose.Schema({
    username: 
    {
        type: 'String'
    },
    password:{
        type: 'String'
    }
  });

  userSchema.pre('save',async function (next){

    if(this.isModified('password')){
        this.password = await bcrypt.hash(this.password, 10);
    }
    next();
  })

  const userModel = mongoose.model('User', userSchema);

  module.exports = userModel;