form: FormGroup;

ngOnInit() {
  this.form = this.fb.group({
    username: ['', [Validators.required, Validators.minLength(5)]],
    password: ['', [Validators.required, Validators.minLength(5)]],
    dpassword: ['', [Validators.required, this.validateMatchPasswords.bind(this)]],
    email: ['', [Validators.required, Validators.email]]
  });
}

validateMatchPasswords(control: FormControl) {
  return {
    error: this.form.get('password') === this.form.get('dpassword')
  };
}

ERROR TypeError: Cannot read property 'get' of undefined
    at RegistrationComponent.validateMatchPasswords (registration.component.ts:32)
    at eval (forms.js:759)
    at Array.map (<anonymous>)
    at _executeValidators (forms.js:759)
    at FormControl.eval [as validator] (forms.js:711)
    at FormControl.AbstractControl._runValidator (forms.js:3433)
    at FormControl.AbstractControl.updateValueAndValidity (forms.js:3387)
    at new FormControl (forms.js:3905)
    at FormBuilder.control (forms.js:7899)
    at FormBuilder._createControl (forms.js:7965)