@NgModule({
 imports: [
 RouterModule,
 RouterModule.forChild(articleRoutes),
 SharedModule,
 ReactiveFormsModule,
 NgbModule.forRoot()
 ],
 declarations: [
 HomeComponent,
 DetailComponent,
 CommentComponent,
 CommentViewComponent
 ],
 providers: [
 HomeService,
 DetailService,
 CommentService
 ]
})
export class ArticleModule { }

public commentForm: FormGroup;
public comment: Comment = new Comment();

constructor(private formBuilder: FormBuilder){}

public formErrors = {
 "nickname": "",
 "email": "",
 "content": "",
 "formError": ""
}

public validationMessages = {
 "nickname": {
 "required": "昵称不能为空",
 },
 "email": {
 "required": "邮箱不能为空",
 "pattern": "请输入正确的邮箱地址"
 },
 "content": {
 "required": "内容不能为空"
 }
}

ngOnInit(): void {
 this.buildForm();
}

private buildForm() {
 this.commentForm = this.formBuilder.group({
 "nickname":[
  this.comment.nickname,
  [
  Validators.required
  ]
 ],
 "email": [
  this.comment.email,
  [
  Validators.required,
  Validators.pattern("^([a-zA-Z0-9_-])+@([a-zA-Z0-9_-])+((\.[a-zA-Z0-9_-]{2,3}){1,2})$")
  ]
 ],
 "content": [
  this.comment.content,
  [
  Validators.required
  ]
 ]
 });
 this.commentForm.valueChanges.subscribe(data => this.onValueChanged(data));
 this.onValueChanged();
}

onValueChanged(data?: any) {
 if (!this.commentForm) {
 return;
 }
 const form = this.commentForm;
 for (const field in this.formErrors) {
 this.formErrors[field] = '';
 const control = form.get(field);
 if (control && control.dirty && !control.valid) {
  const messages = this.validationMessages[field];
  for (const key in control.errors) {
  this.formErrors[field] += messages[key] + ' ';
  }
 }
 }

}

<form [formGroup]="commentForm" (ngSubmit)="sendComment()" role="form" novalidate>
 <div class="control-group">
 <div class="form-group floating-label-form-group controls" [ngClass]="{'has-error': formErrors.nickname}">
  <label>{{ 'comment.nickname' | translate }}</label>
  <input formControlName="nickname" type="text" class="form-control" placeholder="{{ 'comment.nickname' | translate }}">
  <p *ngIf="formErrors.nickname" class="help-block text-danger">
  {{ formErrors.nickname }}
  </p>
 </div>
 </div>
 <div class="control-group" >
 <div class="form-group floating-label-form-group controls" [ngClass]="{'has-error': formErrors.email}">
  <label>{{ 'comment.email' | translate }}</label>
  <input formControlName="email" type="email" class="form-control" placeholder="{{ 'comment.email' | translate }}">
  <p *ngIf="formErrors.email" class="help-block text-danger">
  {{ formErrors.email }}
  </p>
 </div>
 </div>
 <div class="control-group">
 <div class="form-group floating-label-form-group controls" [ngClass]="{'has-error': formErrors.content}">
  <label>{{ 'comment.content' | translate }}</label>
  <textarea formControlName="content" rows="5" class="form-control" placeholder="{{ 'comment.content' | translate }}"></textarea>
  <p *ngIf="formErrors.content" class="help-block text-danger">
  {{ formErrors.content }}
  </p>
 </div>
 </div>
 <p *ngIf="formErrors.formError" class="help-block text-danger">
 {{ formErrors.formError }}
 </p>
 <br>
 <div id="success"></div>
 <div class="form-group">
 <button [disabled]="commentForm.invalid" type="submit" class="btn btn-secondary" >{{ 'comment.submit' | translate }}</button>
 </div>
</form>