How can I implement async validation in Angular CLI?

How can I implement async validation in Angular CLI?

You can implement async validation in Angular by using the AsyncValidatorFn interface. Would you like a code example?

Yes, please provide a code example.

Sure! Here's a simple example:

import { AbstractControl, ValidationErrors, AsyncValidatorFn } from '@angular/forms';
import { Observable, of } from 'rxjs';
import { map, catchError } from 'rxjs/operators';

export function asyncEmailValidator(): AsyncValidatorFn {
  return (control: AbstractControl): Observable<ValidationErrors | null> => {
    return checkEmailExists(control.value).pipe(
      map(emailExists => (emailExists ? { emailTaken: true } : null)),
      catchError(() => of(null))
    );
  };
}

function checkEmailExists(email: string): Observable<boolean> {
  // Simulate an API call to check if the email exists
  return of(email === '[email protected]');
}

You can use this validator in your form control.

How do I use this validator in my form?

You can use the async validator in your form like this:

this.form = this.fb.group({
  email: ['', [Validators.required], [asyncEmailValidator()]],
});

This will apply the async validation to the email field.