Angular 11 Custom ISBN Validator Reactive Forms - angular-material

Question

I'm doing a custom validation for an ISBN number, I already have the function that checks the number and works perfect giving me the response by console, but I need to do the custom validator to get the error in the view with the form control and in this step this error is showing in console when I write an ISBN number, It's like it checks the errors but it doesn't know when its right and it should take the null response as a right ISBN number, at least thats what I saw in some examples.
core.js:6210 ERROR TypeError: Cannot read properties of null (reading 'CheckDigit')
at LibrosComponent_Template (libros.component.html:22)
at executeTemplate (core.js:9600)
at refreshView (core.js:9466)
at refreshComponent (core.js:10637)
at refreshChildComponents (core.js:9263)
at refreshView (core.js:9516)
at refreshEmbeddedViews (core.js:10591)
at refreshView (core.js:9490)
at refreshComponent (core.js:10637)
at refreshChildComponents (core.js:9263)
This is my typescript,
export class LibrosComponent implements OnInit {
//ISBN Validator
isbnValue: string = ""
firstFormGroup: FormGroup;
secondFormGroup: FormGroup;
constructor(
private _formBuilder: FormBuilder,
) {}
ngOnInit() {
this.firstFormGroup = this._formBuilder.group({
tituloControl: ['', Validators.required],
isbnControl: ['', Validators.required],
},
{ validator: this.isbnValidate });
}
isbnValidate(g: FormGroup) {
var isbnValue = g.get('isbnControl').value
var subject = isbnValue;
// Checks for ISBN-10 or ISBN-13 format
var regex = /^(?:ISBN(?:-1[03])?:? )?(?=[0-9X]{10}$|(?=(?:[0-9]+[- ]){3})[- 0-9X]{13}$|97[89][0-9]{10}$|(?=(?:[0-9]+[- ]){4})[- 0-9]{17}$)(?:97[89][- ]?)?[0-9]{1,5}[- ]?[0-9]+[- ]?[0-9]+[- ]?[0-9X]$/;
if (regex.test(subject)) {
// Remove non ISBN digits, then split into an array
var chars = subject.replace(/[- ]|^ISBN(?:-1[03])?:?/g, "").split("");
// Remove the final ISBN digit from `chars`, and assign it to `last`
var last = chars.pop();
var sum = 0;
var check, i;
if (chars.length == 9) {
// Compute the ISBN-10 check digit
chars.reverse();
for (i = 0; i < chars.length; i++) {
sum += (i + 2) * parseInt(chars[i], 10);
}
check = 11 - (sum % 11);
if (check == 10) {
check = "X";
} else if (check == 11) {
check = "0";
}
} else {
// Compute the ISBN-13 check digit
for (i = 0; i < chars.length; i++) {
sum += (i % 2 * 2 + 1) * parseInt(chars[i], 10);
}
check = 10 - (sum % 10);
if (check == 10) {
check = "0";
}
}
if (check != last) {
return null;
} else {
return g.get('isbnControl').setErrors( {CheckDigit: true} )
}
} else {
return g.get('isbnControl').setErrors( {Invalid: true} );
}
}
}
In my HTML I have some inputs that are included in the form:
<form class="form" [formGroup]="firstFormGroup">
<div class="container-1">
<mat-form-field class="width">
<mat-label>Título</mat-label>
<input matInput formControlName="tituloControl" required>
</mat-form-field>
<mat-form-field class="width">
<mat-label>ISBN</mat-label>
<input matInput formControlName="isbnControl" required>
<mat-error *ngIf="firstFormGroup.controls['isbnControl'].pristine || firstFormGroup.controls.isbnControl.errors['CheckDigit']">Invalid ISBN check digit</mat-error>
<mat-error *ngIf="firstFormGroup.controls['isbnControl'].pristine || firstFormGroup.controls.isbnControl.errors['Invalid']">Invalid ISBN</mat-error>
</mat-form-field>
</form>

Answer 1

I already found the solution to the error, replacing the .errors [''] with hasError (''), the .errors[] is to read the property of the object that contains the validation error. But first I have to evaluate with the hasError () method if that property exists to access it.