What properties should be in ng-if so that the method is not called all the time?

Question

Angular

I am using reactive forms in Angular and Angular Material.
I have a mail uniqueness check in the shouldBeUnique() method in which I call the server.
What properties should be in ng-if so that this method is not called all the time.

<mat-error *ngIf="email.valid && email.touched">
            <mat-error *ngIf="shouldBeUnique()">Email is shouldBeUnique</mat-error>
          </mat-error>

Answer 1

Make a variable

_shouldBeUnique = false;
shouldBeUnique(){
request()
.subscribe(res=>(this._shouldBeUnique  = res))
}

and enter the _shouldBeUnique variable into the template