<label>用户名：</label>
 <input type="text" #userNameRef=ngModel [(ngModel)]=userName required>
 <span [style.color]="userNameRef.valid ? 'black':'red'">{{userNameRef.valid}}</span>

<div class="form-group">
 <label>用户名：</label>
 <input type="text" class="form-control" #userNameRef=ngModel minlength="3" maxlength="8" [(ngModel)]=userName required>
 <span [style.color]="userNameRef.valid ? 'black':'red'">{{userNameRef.valid}}</span>
</div>

<div class="form-group">
 <label>用户名：</label>
 <input type="text" class="form-control" #userNameRef=ngModel minlength="3" maxlength="8" [(ngModel)]=userName required>
 <span [style.color]="userNameRef.valid ? 'black':'red'">{{userNameRef.errors|json}}</span>
 <div *ngIf="userNameRef.errors?.required">this is required</div>
<div *ngIf="userNameRef.errors?.minlength">should be 3 chacaters</div>
</div>

<span [style.color]="userNameRef.valid ? 'black':'red'" *ngIf="userNameRef.errors!=null">{{userNameRef.errors|json}}</span>

<form #form="ngForm" (ngSubmit)="form.form.valid && submit(form.value)" novalidate class="form-horizontal" role="form">
 <div class="form-group" [ngClass]="{ 'has-error': form.submitted && !userName.valid }">
  <label class="col-sm-2 control-label">用户名：</label>
  <div class="col-sm-10">
   <input required name="userName" [(ngModel)]="user.userName" #userName="ngModel" type="text" class="form-control" placeholder="请输入用户名...">
   <div *ngIf="form.submitted && !userName.valid" class="text-danger">用户名必须输入！</div>
  </div>
 </div>
 <div class="form-group">
  <label class="col-sm-2 control-label">密码：</label>
  <div class="col-sm-10" [ngClass]="{'has-error': form.submitted && !password.valid }">
   <input required minlength="8" maxlength="12" [(ngModel)]="user.password" name="password" #password="ngModel" type="password" class="form-control" placeholder="请输入密码...">
   <div *ngIf="form.submitted && !password.valid" class="text-danger">密码必须输入,至少要8位！</div>
  </div>
 </div>
 <div class="form-group">
  <div class="col-sm-offset-2 col-sm-10">
   <button type="submit" class="btn btn-success">登录</button>
  </div>
 </div>
</form>

import { Component, OnInit} from '@angular/core';
import{UserModel} from '../model/user.model';//引入了usermodel
@Component({
 selector: 'app-login',
 templateUrl: './login.component.html',
 styleUrls: ['./login.component.css']
})
export class LoginComponent implements OnInit {
 constructor() { }
 //定义user为Usermodel
 private user=new UserModel();
 ngOnInit() {
 }
/**
 * 登陆事件
 * @param form 表单中的输入值
 */
 submit(form){
 if(form.username=="1"&&form.password=="12345678"){
  alert("登录成功了");
 }else{
  alert("非法用户");
 }
 }
}

export class UserModel{
 userName:string;
 password:string;
}