angular 5 template forms detect change of form validity status

Question

are reactive forms the way to go in order to have a component that can listen for changes in the validity status of the form it contains and execute some compoment\'s method

Answer 1

You can do something like this do detect a validity change and execute a method based on whether the form is VALID or INVALID.

this.myForm.statusChanges
  .subscribe(val => this.onFormValidation(val));

onFormValidation(validity: string) {
  switch (validity) {
    case "VALID":
      // do 'form valid' action
      break;
    case "INVALID":
      // do 'form invalid' action
      break;
  }
}

Answer 2

If you want to get only the status and not the value you can use statusChanges:

export class Component {

    @ViewChild('myForm') myForm;

    this.myForm.statusChanges.subscribe(
        result => console.log(result)
    );
}

If you even want data changes, you can subscribe to the valueChanges of the form and check the status of the form using this.myForm.status:

export class Component {

    @ViewChild('myForm') myForm;

    this.myForm.valueChanges.subscribe(
        result => console.log(this.myForm.status)
    );
}

Possible values of status are: VALID, INVALID, PENDING, or DISABLED.

Here is the reference for the same

Answer 3

You can subscribe to the whole form changes and implement your logic there.

@ViewChild('myForm') myForm;

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