The valueChanges observable in Angular's FormControl or FormGroup can still be triggered even when you use { emitEvent: false, onlySelf: true }. Here's why:
emitEvent: false: This option prevents the valueChanges observable of the specific control (or group) from emitting events when the value is programmatically set using setValue, patchValue, or similar methods. However, it does not prevent parent forms' valueChanges from being triggered if they depend on the child control.
onlySelf: true: This option ensures that only the targeted control's state is updated, and the parent controls are not affected by the change. However, it does not directly stop the valueChanges observable from emitting events.
Why valueChanges Still Triggers
Even with { emitEvent: false }, Angular’s change detection might still notify parent controls or other parts of the form tree if they listen for changes in any related control. This can sometimes be misunderstood as the child control's valueChanges emitting when it actually isn't.
How to Handle This
If you don't want valueChanges to trigger, double-check:
1. Where the subscription is made: Ensure the subscription isn't on the parent form, which could be reacting to child updates.
2. Avoid unintended updates: Use the emitEvent option properly and confirm that no external code updates the control value or triggers change detection indirectly.
For debugging:
Log when the valueChanges observable emits and verify which control (or group) triggered the event.
Ensure no other parts of your application are subscribing to parent FormGroup changes and reacting unexpectedly.
emitEvent: false: This option prevents the valueChanges observable of the specific control (or group) from emitting events when the value is programmatically set using setValue, patchValue, or similar methods. However, it does not prevent parent forms' valueChanges from being triggered if they depend on the child control.
onlySelf: true: This option ensures that only the targeted control's state is updated, and the parent controls are not affected by the change. However, it does not directly stop the valueChanges observable from emitting events.
Why valueChanges Still Triggers
Even with { emitEvent: false }, Angular’s change detection might still notify parent controls or other parts of the form tree if they listen for changes in any related control. This can sometimes be misunderstood as the child control's valueChanges emitting when it actually isn't.
How to Handle This
If you don't want valueChanges to trigger, double-check:
1. Where the subscription is made: Ensure the subscription isn't on the parent form, which could be reacting to child updates.
2. Avoid unintended updates: Use the emitEvent option properly and confirm that no external code updates the control value or triggers change detection indirectly.
For debugging:
Log when the valueChanges observable emits and verify which control (or group) triggered the event.
Ensure no other parts of your application are subscribing to parent FormGroup changes and reacting unexpectedly.