Mongoose instance method `this` does not refer to model

Question

EDIT: I have discovered that console.log(this) ran inside the setPassword method returns only the hash and salt. I'm not sure why this is happening, however it indicates that this is not refering to the model as it should.

---

I have the following schema with the following instance method:

let userSchema = new mongoose.Schema({
  username: {type: String, required: true},
  email: {type: String, required: true, index: {unique: true}},
  joinDate: {type: Date, default: Date.now},
  clips: [clipSchema],
  hash: {type: String},
  salt: {type: String}
})

userSchema.methods.setPassword = (password) => {
  this.salt = crypto.randomBytes(32).toString('hex')
  this.hash = crypto.pbkdf2Sync(password, this.salt, 100000, 512, 'sha512').toString('hex')
}

The instance method is called here, then the user is saved:

let user = new User()

user.username = req.body.username
user.email = req.body.email
user.setPassword(req.body.password)

user.save((err) => {
  if (err) {
    sendJsonResponse(res, 404, err)
  } else {
    let token = user.generateJwt()
    sendJsonResponse(res, 200, { 'token': token })
  }
})

However, when I view the users collection in the mongo CLI, there is no mention of hash or salt.

{
 "_id" : ObjectId("576338b363bb7df7024c044b"),
 "email" : "[email protected]",
 "username" : "Bob",
 "clips" : [ ],
 "joinDate" : ISODate("2016-06-16T23:39:31.825Z"),
 "__v" : 0 
}

Answer 1

The reason it was not working was because I was using an arrow method. I had to make it a normal function:

userSchema.methods.setPassword = function (password) {

The reason is because arrow functions treat this differently from regular functions. Please see the following for more detail:

http://exploringjs.com/es6/ch_arrow-functions.html