Angular Web Framework Reactive Forms & Validation 4

Question 1

Which `FormBuilder` shorthand creates a control with an initial value and a single validator?

Accepted Answer

fb.control('value', Validators.required)

Answer

`FormBuilder.control(initialValue, validators)` is the shorthand for creating a single reactive FormControl.

Question 2

When composing multiple validators with `Validators.compose()`, what happens if one validator returns errors?

Accepted Answer

All validator errors are merged into a single error object

Answer

`Validators.compose()` runs all validators and merges their error objects, so multiple errors can coexist.

Question 3

What is the difference between `setValue()` and `patchValue()` on a FormGroup?

Accepted Answer

setValue() requires all controls to be provided; patchValue() allows partial updates

Answer

`setValue()` requires an object with keys matching every control, while `patchValue()` only updates the provided keys.

Question 4

How can you run async validators only after all synchronous validators pass?

Accepted Answer

Angular does this automatically — async validators are skipped when sync validators fail

Answer

Angular's built-in behavior is to skip async validators entirely when any synchronous validator returns an error.

Question 5

Which observable on a FormControl emits only when the control's validation status changes?

Accepted Answer

statusChanges

Answer

`statusChanges` emits the new status string ('VALID', 'INVALID', 'PENDING', 'DISABLED') whenever it changes.

Angular Web Framework Practice Test