user.js

// models/user.js
// ...

UserSchema.pre("save", async function hashPassword(next) {
  if (!this.isModified("password")) next();

  this.password = await bcrypt.hash(this.password, 8);
});

UserSchema.methods = {
  compareHash(hash) {
    return bcrypt.compare(hash, this.password);
  },

  generateToken() {
    return jwt.sign({ id: this.id }, "secret", {
      expiresIn: 86400
    });
  }
};

// ...