feat(forms): add updateOn blur option to FormControls (#18408)

By default, the value and validation status of a `FormControl` updates
whenever its value changes. If an application has heavy validation
requirements, updating on every text change can sometimes be too expensive.

This commit introduces a new option that improves performance by delaying
form control updates until the "blur" event.  To use it, set the `updateOn`
option to `blur` when instantiating the `FormControl`.

```ts
// example without validators
const c = new FormControl(, { updateOn: blur });

// example with validators
const c= new FormControl(, {
   validators: Validators.required,
   updateOn: blur
});
```

Like in AngularJS, setting `updateOn` to `blur` will delay the update of
the value as well as the validation status. Updating value and validity
together keeps the system easy to reason about, as the two will always be
in sync. It's  also worth noting that the value/validation pipeline does
still run when the form is initialized (in order to support initial values).

Closes #7113

packages/forms/test/reactive_integration_spec.ts

@@ -731,6 +731,181 @@ export function main() {
 
     });
 
+    describe('updateOn options', () => {
+
+      describe('on blur', () => {
+
+        it('should not update value or validity based on user input until blur', () => {
+          const fixture = initTest(FormControlComp);
+          const control = new FormControl('', {validators: Validators.required, updateOn: 'blur'});
+          fixture.componentInstance.control = control;
+          fixture.detectChanges();
+
+          const input = fixture.debugElement.query(By.css('input')).nativeElement;
+          input.value = 'Nancy';
+          dispatchEvent(input, 'input');
+          fixture.detectChanges();
+
+          expect(control.value).toEqual('', 'Expected value to remain unchanged until blur.');
+          expect(control.valid).toBe(false, 'Expected no validation to occur until blur.');
+
+          dispatchEvent(input, 'blur');
+          fixture.detectChanges();
+
+          expect(control.value)
+              .toEqual('Nancy', 'Expected value to change once control is blurred.');
+          expect(control.valid).toBe(true, 'Expected validation to run once control is blurred.');
+        });
+
+        it('should not update parent group value/validity from child until blur', () => {
+          const fixture = initTest(FormGroupComp);
+          const form = new FormGroup(
+              {login: new FormControl('', {validators: Validators.required, updateOn: 'blur'})});
+          fixture.componentInstance.form = form;
+          fixture.detectChanges();
+
+          const input = fixture.debugElement.query(By.css('input')).nativeElement;
+          input.value = 'Nancy';
+          dispatchEvent(input, 'input');
+          fixture.detectChanges();
+
+          expect(form.value)
+              .toEqual({login: ''}, 'Expected group value to remain unchanged until blur.');
+          expect(form.valid).toBe(false, 'Expected no validation to occur on group until blur.');
+
+          dispatchEvent(input, 'blur');
+          fixture.detectChanges();
+
+          expect(form.value)
+              .toEqual({login: 'Nancy'}, 'Expected group value to change once input blurred.');
+          expect(form.valid).toBe(true, 'Expected validation to run once input blurred.');
+        });
+
+        it('should not wait for blur event to update if value is set programmatically', () => {
+          const fixture = initTest(FormControlComp);
+          const control = new FormControl('', {validators: Validators.required, updateOn: 'blur'});
+          fixture.componentInstance.control = control;
+          fixture.detectChanges();
+
+          control.setValue('Nancy');
+          fixture.detectChanges();
+
+          const input = fixture.debugElement.query(By.css('input')).nativeElement;
+          expect(input.value).toEqual('Nancy', 'Expected value to propagate to view immediately.');
+          expect(control.value).toEqual('Nancy', 'Expected model value to update immediately.');
+          expect(control.valid).toBe(true, 'Expected validation to run immediately.');
+        });
+
+        it('should not update dirty state until control is blurred', () => {
+          const fixture = initTest(FormControlComp);
+          const control = new FormControl('', {updateOn: 'blur'});
+          fixture.componentInstance.control = control;
+          fixture.detectChanges();
+
+          expect(control.dirty).toBe(false, 'Expected control to start out pristine.');
+
+          const input = fixture.debugElement.query(By.css('input')).nativeElement;
+          input.value = 'Nancy';
+          dispatchEvent(input, 'input');
+          fixture.detectChanges();
+
+          expect(control.dirty).toBe(false, 'Expected control to stay pristine until blurred.');
+
+          dispatchEvent(input, 'blur');
+          fixture.detectChanges();
+
+          expect(control.dirty).toBe(true, 'Expected control to update dirty state when blurred.');
+        });
+
+        it('should continue waiting for blur to update if previously blurred', () => {
+          const fixture = initTest(FormControlComp);
+          const control =
+              new FormControl('Nancy', {validators: Validators.required, updateOn: 'blur'});
+          fixture.componentInstance.control = control;
+          fixture.detectChanges();
+
+          const input = fixture.debugElement.query(By.css('input')).nativeElement;
+          dispatchEvent(input, 'blur');
+          fixture.detectChanges();
+
+          dispatchEvent(input, 'focus');
+          input.value = '';
+          dispatchEvent(input, 'input');
+          fixture.detectChanges();
+
+          expect(control.value)
+              .toEqual('Nancy', 'Expected value to remain unchanged until second blur.');
+          expect(control.valid).toBe(true, 'Expected validation not to run until second blur.');
+
+          dispatchEvent(input, 'blur');
+          fixture.detectChanges();
+
+          expect(control.value).toEqual('', 'Expected value to update when blur occurs again.');
+          expect(control.valid).toBe(false, 'Expected validation to run when blur occurs again.');
+        });
+
+        it('should not use stale pending value if value set programmatically', () => {
+          const fixture = initTest(FormControlComp);
+          const control = new FormControl('', {validators: Validators.required, updateOn: 'blur'});
+          fixture.componentInstance.control = control;
+          fixture.detectChanges();
+
+          const input = fixture.debugElement.query(By.css('input')).nativeElement;
+          input.value = 'aa';
+          dispatchEvent(input, 'input');
+          fixture.detectChanges();
+
+          control.setValue('Nancy');
+          fixture.detectChanges();
+
+          dispatchEvent(input, 'blur');
+          fixture.detectChanges();
+
+          expect(input.value).toEqual('Nancy', 'Expected programmatic value to stick after blur.');
+        });
+
+        it('should set initial value and validity on init', () => {
+          const fixture = initTest(FormControlComp);
+          const control =
+              new FormControl('Nancy', {validators: Validators.maxLength(3), updateOn: 'blur'});
+          fixture.componentInstance.control = control;
+          fixture.detectChanges();
+
+          const input = fixture.debugElement.query(By.css('input')).nativeElement;
+
+          expect(input.value).toEqual('Nancy', 'Expected value to be set in the view.');
+          expect(control.value).toEqual('Nancy', 'Expected initial model value to be set.');
+          expect(control.valid).toBe(false, 'Expected validation to run on initial value.');
+        });
+
+        it('should reset properly', () => {
+          const fixture = initTest(FormControlComp);
+          const control = new FormControl('', {validators: Validators.required, updateOn: 'blur'});
+          fixture.componentInstance.control = control;
+          fixture.detectChanges();
+
+          const input = fixture.debugElement.query(By.css('input')).nativeElement;
+          input.value = 'aa';
+          dispatchEvent(input, 'input');
+          fixture.detectChanges();
+
+          dispatchEvent(input, 'blur');
+          fixture.detectChanges();
+          expect(control.dirty).toBe(true, 'Expected control to be dirty on blur.');
+
+          control.reset();
+
+          dispatchEvent(input, 'blur');
+          fixture.detectChanges();
+
+          expect(control.dirty).toBe(false, 'Expected pending dirty value to reset.');
+          expect(control.value).toBe(null, 'Expected pending value to reset.');
+        });
+
+      });
+
+    });
+
     describe('ngModel interactions', () => {
 
       it('should support ngModel for complex forms', fakeAsync(() => {
@@ -1238,14 +1413,14 @@ export function main() {
         TestBed.overrideComponent(FormGroupComp, {
           set: {
             template: `
-         <div [formGroup]="myGroup">
+         <div [formGroup]="form">
            <input type="text" [(ngModel)]="data">
          </div>
         `
           }
         });
         const fixture = initTest(FormGroupComp);
-        fixture.componentInstance.myGroup = new FormGroup({});
+        fixture.componentInstance.form = new FormGroup({});
 
         expect(() => fixture.detectChanges())
             .toThrowError(new RegExp(
@@ -1256,14 +1431,14 @@ export function main() {
         TestBed.overrideComponent(FormGroupComp, {
           set: {
             template: `
-         <div [formGroup]="myGroup">
+         <div [formGroup]="form">
             <input type="text" [(ngModel)]="data" [ngModelOptions]="{standalone: true}">
          </div>
         `
           }
         });
         const fixture = initTest(FormGroupComp);
-        fixture.componentInstance.myGroup = new FormGroup({});
+        fixture.componentInstance.form = new FormGroup({});
 
         expect(() => fixture.detectChanges()).not.toThrowError();
       });
@@ -1272,7 +1447,7 @@ export function main() {
         TestBed.overrideComponent(FormGroupComp, {
           set: {
             template: `
-          <div [formGroup]="myGroup">
+          <div [formGroup]="form">
             <div formGroupName="person">
               <input type="text" [(ngModel)]="data">
             </div>
@@ -1281,8 +1456,7 @@ export function main() {
           }
         });
         const fixture = initTest(FormGroupComp);
-        const myGroup = new FormGroup({person: new FormGroup({})});
-        fixture.componentInstance.myGroup = new FormGroup({person: new FormGroup({})});
+        fixture.componentInstance.form = new FormGroup({person: new FormGroup({})});
 
         expect(() => fixture.detectChanges())
             .toThrowError(new RegExp(
@@ -1293,7 +1467,7 @@ export function main() {
         TestBed.overrideComponent(FormGroupComp, {
           set: {
             template: `
-          <div [formGroup]="myGroup">
+          <div [formGroup]="form">
             <div ngModelGroup="person">
               <input type="text" [(ngModel)]="data">
             </div>
@@ -1302,7 +1476,7 @@ export function main() {
           }
         });
         const fixture = initTest(FormGroupComp);
-        fixture.componentInstance.myGroup = new FormGroup({});
+        fixture.componentInstance.form = new FormGroup({});
 
         expect(() => fixture.detectChanges())
             .toThrowError(
@@ -1406,7 +1580,9 @@ export function main() {
         // formControl should update normally
         expect(fixture.componentInstance.control.value).toEqual('updatedValue');
       });
+
     });
+
   });
 }
 
@@ -1470,7 +1646,6 @@ class FormControlComp {
 class FormGroupComp {
   control: FormControl;
   form: FormGroup;
-  myGroup: FormGroup;
   event: Event;
 }