agular active form validation code example

Example 1: custom validator

import {AbstractControl, ValidatorFn} from '@angular/forms';

export function blue(): ValidatorFn {  
    return (control: AbstractControl): { [key: string]: any } | null =>  
        control.value?.toLowerCase() === 'blue' 
            ? null : {wrongColor: control.value};
}
<>

Example 2: validation minlength angular

Validators.minLength(9)