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These docs state the following:
If emitEvent is true, this change will cause a valueChanges event on the FormControl to be emitted. This defaults to true (as it falls through to updateValueAndValidity).
What is this updateValueAndValidity?
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Descriptionlink. It provides some of the shared behavior that all controls and groups of controls have, like running validators, calculating status, and resetting state. It also defines the properties that are shared between all sub-classes, like value , valid , and dirty . It shouldn't be instantiated directly.
SetValue Vs PatchValue The difference is that with setValue we must include all the controls, while with the patchValue you can exclude some controls.
The ValueChanges is an event raised by the Angular forms whenever the value of the FormControl, FormGroup or FormArray changes. It returns an observable so that you can subscribe to it. The observable gets the latest value of the control. It allows us to track changes made to the value in real-time and respond to it.
emitEvent is an event triggered when our form value or status changes. Hence in official documentation: *emitEvent: When true or not supplied (the default), both the `statusChanges` and `valueChanges` observables emit events with the latest status and value when the control value is updated.
You can subscribe to value changes of a control or the whole form.
updateValueAndValidity allows you to modify the value of one or more form controls and the flag allows you to specify if you want this to emit the value to valueChanges subscribers.
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