如何使用Angular reactive Form的Typescript声明模型类

export class User {
  firstName: string;
  lastName: string;
  email: string;
  password: string;
}

import { Component, OnInit } from '@angular/core';
import { FormBuilder, FormGroup } from '@angular/forms';
import { User } from './user.model';

@Component({
  selector: 'app-user-form',
  templateUrl: './user-form.component.html',
  styleUrls: ['./user-form.component.css']
})
export class UserFormComponent implements OnInit {
  userForm: FormGroup;
  user: User;

  constructor(private formBuilder: FormBuilder) { }

  ngOnInit() {
    this.user = new User();
    this.userForm = this.formBuilder.group({
      firstName: [this.user.firstName],
      lastName: [this.user.lastName],
      email: [this.user.email],
      password: [this.user.password]
    });
  }

  onSubmit() {
    // 处理表单提交
  }
}

<form [formGroup]="userForm" (ngSubmit)="onSubmit()">
  <label for="firstName">First Name:</label>
  <input type="text" id="firstName" formControlName="firstName">

  <label for="lastName">Last Name:</label>
  <input type="text" id="lastName" formControlName="lastName">

  <label for="email">Email:</label>
  <input type="email" id="email" formControlName="email">

  <label for="password">Password:</label>
  <input type="password" id="password" formControlName="password">

  <button type="submit">Submit</button>
</form>