this.signupForm = this.fb.group({
 userName: ['', [Validators.required, Validators.minLength(3)]],
 email: ['', [Validators.required, Validators.pattern('[a-z0-9._%+_]+@[a-z0-9.-]+')]]
});

myControl.setValidators(Validators.required);
myControl.setValidators([Validators.required, Validators.maxLength(6)]);

myControl.clearValidators();
myControl.updateValueAndValidity();

function myCustomValidator(c: AbstractControl): 
 {[key: string]: boolean} | null {
 if(somethingIsWrong) {
  return { 'myvalidator': true};
 }
 return null;
}

function myCustomValidator(param: any): ValidatorFn {
 return (c: AbstractControl): {[key: string]: boolean} | null {
  if(somethingIsWrong) {
   return { 'myvalidator': true};
  }
   return null;
 }
}

function emailMatcher(c: AbstractControl) {
 let emailControl = c.get('email');
 let confirmControl = c.get('confirmEmail');

 if (emailControl.pristine || confirmControl.pristine) {
  return null;
 }

 return emailControl.value === confirmControl.value ? null : { 'match': true };
}

ngOnInit(): void {
 this.signupForm = this.fb.group({
  userName: ['', [Validators.required, Validators.minLength(6)]],
  emailGroup: this.fb.group({
   email: ['', [Validators.required, Validators.email]],
   confirmEmail: ['', [Validators.required]],
  }, { validator: emailMatcher })
});

<div class="form-group">
  <div class="col-md-offset-1 col-md-8 checkbox">
   开启手机登录
   <label>
     <input type="radio" value="1"
      formControlName="enableMobile">
       是
   </label>
   <label>
     <input type="radio" value="0"
      formControlName="enableMobile">
       否
   </label>
  </div>
</div>

<div class="form-group"
  [ngClass]="{'has-error': (mobile.touched || mobile.dirty) && !mobile.valid }">
     <label class="col-md-2 control-label"
         for="mobileId">手机号码</label>

     <div class="col-md-8">
      <input class="form-control"
          id="mobileId"
          type="text"
          placeholder="请输入手机号码"
          formControlName="mobile"/>
      <span class="help-block" *ngIf="(mobile.touched || mobile.dirty) 
        && mobile.errors">
         <span *ngIf="mobile.errors.required">
           请输入手机号码
         </span>
         <span *ngIf="mobile.errors.minlength">
           手机号码格式不正确
         </span>
      </span>
     </div>
</div>

ngOnInit(): void {
  ...
  this.signupForm.get('enableMobile').valueChanges
   .subscribe(value => this.checkMobile(value));
}

checkMobile(enableMobile: string): void {
 const mobileControl = this.signupForm.get('mobile');
 
 enableMobile === "1" ? 
   mobileControl.setValidators([Validators.required,
    Validators.pattern('1(3|4|5|7|8)\\d{9}')]) :
   mobileControl.clearValidators();
 
  mobileControl.updateValueAndValidity();
}

<div class="form-group"
  [ngClass]="{'has-error': (age.touched || age.dirty) && !age.valid }">
  <label class="col-md-2 control-label"
   for="ageId">年龄</label>

   <div class="col-md-8">
     <input class="form-control"
         id="ageId"
         type="number"
         placeholder="请输入年龄"
         formControlName="age"/>
     <span class="help-block" *ngIf="(age.touched || age.dirty) && age.errors">
         <span *ngIf="age.errors.range">
           输入年龄不合法
         </span>
     </span>
   </div>
</div>

function myCustomValidator(c: AbstractControl): 
 {[key: string]: boolean} | null {
 if(somethingIsWrong) {
  return { 'myvalidator': true};
 }
 return null;
}

function ageValidator(c: AbstractControl): { [key: string]: any } | null {
 let age = c.value;
 if (age && (isNaN(age) || age < 20 || age > 120)) {
  return { 'range': true, min: 20, max: 120 };
 }
 return null;
}

ngOnInit(): void {
 this.signupForm = this.fb.group({
  // ...
  age: ['', ageValidator]
 });
}

function myCustomValidator(param: any): ValidatorFn {
 return (c: AbstractControl): {[key: string]: boolean} | null {
  if(somethingIsWrong) {
   return { 'myvalidator': true};
  }
   return null;
 }
}

function ageRange(min: number, max: number): ValidatorFn {
 return (c: AbstractControl): { [key: string]: any } | null => {
  let age = c.value;
  if (age && (isNaN(age) || age < min || age > max)) {
   return { 'range': true, min: min, max: max };
  }
  return null;
 }
}

ngOnInit(): void {
 this.signupForm = this.fb.group({
  // ...
  age: ['', ageRange(20, 120)]
 });
}

<label class="col-md-2 control-label"
    for="emailId">确认邮箱</label>
<div class="col-md-8">
   <input class="form-control"
      id="confirmEmailId"
      type="email"
      placeholder="请再次输入邮箱地址"
      formControlName="confirmEmail"/>
   <span class="help-block" *ngIf="(confirmEmail.touched || 
      confirmEmail.dirty)">
      <span *ngIf="confirmEmail.errors?.required">
        请输入邮箱地址
      </span>
      <span *ngIf="!confirmEmail.errors?.required && 
        emailGroup.errors?.match">
        两次输入的邮箱地址不一致
      </span>
   </span>
</div>

function emailMatcher(c: AbstractControl) {
 let emailControl = c.get('email');
 let confirmControl = c.get('confirmEmail');
 if (emailControl.pristine || confirmControl.pristine) {
  return null;
 }
 return emailControl.value === confirmControl.value ? null : { 'match': true };
}

ngOnInit(): void {
 this.signupForm = this.fb.group({
  userName: ['', [Validators.required, Validators.minLength(6)]],
  emailGroup: this.fb.group({
   email: ['', [Validators.required, Validators.email]],
   confirmEmail: ['', [Validators.required]],
  }, { validator: emailMatcher }),
  // ...
});

<div class="form-group"
   formGroupName="emailGroup"
   [ngClass]="{'has-error': emailGroup.errors }">
     <label class="col-md-2 control-label"
         for="emailId">邮箱</label>
     <div class="col-md-8">
      <input class="form-control"
          id="emailId"
          type="email"
          placeholder="请输入邮箱地址"
          formControlName="email"/>
      <span class="help-block" *ngIf="(email.touched || email.dirty) &&
         email.errors">
         <span *ngIf="email.errors.required">
           请输入邮箱地址
         </span>
         <span *ngIf="!email.errors.required && email.errors.email">
           请输入有效的邮箱地址
         </span>
      </span>
     </div>
     <!--其余部分：请参考"新增email控件"的内容-->
</div>

this.signupForm = this.fb.group({
  userName: ['', [Validators.required, Validators.minLength(6)]],
  emailGroup: this.fb.group({
   email: ['', [Validators.required, Validators.email]],
   confirmEmail: ['', [Validators.required]],
}, { validator: emailMatcher })

<div class="form-group" formGroupName="emailGroup"
  [ngClass]="{'has-error': emailGroup.errors }">

<span *ngIf="!confirmEmail.errors?.required && emailGroup.errors?.match">
  两次输入的邮箱地址不一致
</span>

export class AppComponent {
 constructor(private fb: FormBuilder) {
  this.form = fb.group({
   name: 'semlinker',
   age: 31
  });

  this.form.valueChanges.subscribe(data => {
   console.log('Form changes', data)
  });
 }
}

<form #myForm="ngForm" (ngSubmit)="onSubmit()">
 <input type="text"
  name="name" 
  class="form-control" 
  required   
  [(ngModel)]="user.name">
 <input type="number" 
   name="age" 
   class="form-control" 
   required 
  [(ngModel)]="user.age">
</form>

class AppComponent implements AfterViewInit {
 @ViewChild('myForm') form;

 ngAfterViewInit() {
  this.form.control.valueChanges
   .debounceTime(500)
   .subscribe(values => this.doSomething(values));
 }
}