Example of using bcrypt with mongoose middleware to enforce password hashing with bcrypt on save.

user.js

var mongoose = require('mongoose'),                                                                                                                                            
    Schema = mongoose.Schema                                                                                                                                                                                                                                                                                                                                
                                                                                                                                                                               
var bcrypt = require('bcrypt')                                                                                                                                                 
                                                                                                                                                                                                                                                                                                                                                              
var UserSchema = new Schema( {                                                                                                                                                 
    email: String,                                                                                                                                                             
    password: String                                                                                                                                                           
} )                                                                                                                                                                                                                                                                                                                                                          
                                                                                                                                                                               
// pre                                                                                                                                                                         
UserSchema.pre('save', function(next) {                                                                                                                                        
    if(this.password) {                                                                                                                                                        
        var salt = bcrypt.genSaltSync(10)                                                                                                                                     
        this.password  = bcrypt.hashSync(this.password, salt)                                                                                                                
    }                                                                                                                                                                          
    next()                                                                                                                                                                     
})                                                                                                                                                                                                                                                                                                                                                          
                                                                                                                                                                               
mongoose.model('User', UserSchema);

myoussef3030 thanks for the great snippet works perfectly.

userSchema.pre('save', async function (next) {
const user = this;
if (user.isModified('password')) {
user.password = await bcrypt.hash(user.password, 8)
}
next()
})
for a readability we can also user variable like this

For anybody who might need this for readability and clarity, better to use "isModified" so that when the password is updated, we don't have to re-hash again multiple times.

userSchema.pre("save", async function(next){
if(this.isModified("password")){
this.password = await bcrypt.hash(this.password, 8)
}
next();
});