user.comparePassword не является функцией

const mongoose = require('mongoose');
var bcrypt = require('bcrypt-nodejs');
SALT_WORK_FACTOR = 10;

const userDataModal = mongoose.Schema({
    username: {
        type: String,
        required : true,
        unique:true
    },
    password: {
        type: String,
        required : true
    }

});

userDataModal.pre('save', function(next) {
    var user = this;

    // only hash the password if it has been modified (or is new)
    if (!user.isModified('password')) return next();

    // generate a salt
    bcrypt.genSalt(SALT_WORK_FACTOR, function(err, salt) {
        if (err) return next(err);

        // hash the password using our new salt
        bcrypt.hash(user.password, salt, null, function(err, hash) {
            if (err) return next(err);

            // override the cleartext password with the hashed one
            user.password = hash;
            next();
        });
    });
});

userDataModal.methods.comparePassword = function(candidatePassword, cb) {
    bcrypt.compare(candidatePassword, this.password, function(err, isMatch) {
        if (err) return cb(err);
        cb(null, isMatch);
    });
};


// Users.index({ emaiId: "emaiId", fname : "fname", lname: "lname" });

const userDatamodal = module.exports = mongoose.model("usertemplates" , userDataModal)



//inserting document
     userDataModel.findOne({ username: reqData.username }).then(doc => {
            console.log(doc)
            if (doc == null) {
                let userDataMode = new userDataModel(reqData);
               // userDataMode.password = userDataMode.generateHash(reqData.password);
                userDataMode.save({new:true}).then(data=>{
                          let obj={
                              success:true,
                              message: "New user registered successfully",
                              data:data
                          }
                            resolve(obj)
                }).catch(err=>{
                                reject(err)
                })

            }
            else {
                resolve({
                    success: true,
                    docExists: true,
                    message: "already user registered",
                    data: doc
                }
                )
            }

        }).catch(err => {
            console.log(err)
            reject(err)
        })

//retriving and checking
      // test a matching password
                user.comparePassword(requestData.password, function(err, isMatch) {
                    if (err){ 

                        reject({
                            'status': 'Error',
                            'data': err
                        });

                        throw err;
                    } else  {
                        if(isMatch){

                            resolve({   
                                'status': true,
                                'data': user,
                                'loginStatus' : "successfully Login"
                            });

                            console.log('Password123:', isMatch); // -> Password123: true

                        }