async-validator | validate form | Validation library

I followed the short guide on Angular's website for Creating asynchronous validators that can be found at this url.

https://angular.io/guide/form-validation#implementing-a-custom-async-validator

As a result, I have this code:

I'm trying to force an update on the validators of all the form groups of a custom stepper just before the registration at the end of the final step, like so :

I'm trying to make a custom AsyncValidatorFn that will send a post request to the node.js/express server only after the user has finished typing in his email/username to check if it is unique, kinda like how Validators.required only pops up the error after you've clicked the input field, and then clicked out, without typing anything in.

I used this guide to help me start out and this is what I have for now:

• In the form group in the component:

  ...