Execute method after validation. Ionic 4

Hi everyone
I need execute a method when a form control its validated.
i tested (ionChange) with debounce and it runs without validating the control after the specified time. therefore the validation shows the control in red, but after the time it executes the method.
How could I execute the method once validated in form control?
I hope everyone understands my need.
Best regards.
Joaquín.

Maybe I should explain better.
I have a form, and I need that after validating the input component, a method is executed.
I have the following:

    <ion-item>
      <ion-label position="floating">Number</ion-label>
      <ion-input type="number" formControlName="number"></ion-input>
    </ion-item>

and in the validation:

      number: new FormControl('', Validators.compose([
        Validators.required,
        Validators.pattern('^[0-9]{7,8}$')
      ])),

this works and is marked in green when there is a 7 or 8 digit number.
I need to know the status of the validation and, if it is true, call the method, the method should return data and fill in the other components.
This must occur before submit.
Is all this possible?
Thanks.

You could probably do it using a custom async validator.

I have an example here. (With a link to the source code)

An async validator is executed after other validators, and although it is defined as a “validation” technique, you could probably write your code here?