Is there a way to validate an input field and display error messages using a TypeScript file instead of directly in the HTML file within Angular 4?

Question

Is there a way to validate an input field and display error messages using a TypeScript file instead of directly in the HTML file within Angular 4?

I am just starting out with Angular, so please bear with me if my question seems basic. I'm eager to learn and hopeful that I can find the answers I need here.

Currently, I have implemented validation for an input field that captures a user's First Name, and it is functioning correctly.

I am wondering why all these validations and error messages are in my HTML file.

If possible, could someone guide me on how to move this logic to the TypeScript file? Or perhaps correct any misunderstandings I may have.

Here is the code snippet:

<mat-form-field appearance="outline" class="col-sm-6">
                        <mat-label>First Name</mat-label>
                        <input matInput minlength="4" pattern="^[a-z]*$" maxlength="15" [formControl]="fName" required>
                        <mat-error *ngIf="fName.errors?.required">Please fill out this field</mat-error>
                        <mat-error *ngIf="fName.errors&&fName.errors?.minlength">Required minimum 4 characters</mat-error>
                        <mat-error *ngIf="fName.errors&&fName.errors.pattern">Enter only alphabets</mat-error>
                      </mat-form-field>

TypeScript:

fName = new FormControl();

The current setup works, but I am curious to know if achieving the same functionality from the TypeScript file is possible.

Apologies if my question is taking up your precious time.

angular typescript angular-material

Answer 1

Answer №1

If you want to track the changes of a form, you can do so by subscribing to the valueChanges observable of the form like this:

myForm: FormGroup;

this.myForm.valueChanges.subscribe(()=> { 
    // Handle form value changes here.
    // You can assign custom error messages to variables like this.fnameErrorMsg for specific fields
})

You can also define custom error messages and store them in variables such as {{fnameErrorMsg}}.

To see an example of a reactive form that I've developed, you can check out my GitHub profile here. While it may not have exactly what you need, it can serve as a reference for working with forms.

<mat-error *ngIf="!myForm.controls['fName'].valid">{{fnameErrorMsg}}</mat-error>

Answer 2

If you want to track the changes of a form, you can do so by subscribing to the valueChanges observable of the form like this:

myForm: FormGroup;

this.myForm.valueChanges.subscribe(()=> { 
    // Handle form value changes here.
    // You can assign custom error messages to variables like this.fnameErrorMsg for specific fields
})

You can also define custom error messages and store them in variables such as {{fnameErrorMsg}}.

To see an example of a reactive form that I've developed, you can check out my GitHub profile here. While it may not have exactly what you need, it can serve as a reference for working with forms.

<mat-error *ngIf="!myForm.controls['fName'].valid">{{fnameErrorMsg}}</mat-error>

Is there a way to validate an input field and display error messages using a TypeScript file instead of directly in the HTML file within Angular 4?

Answer №1

Similar questions

Activate the reactive forms when the checkbox is selected

arranging data in html table columns using angular 2

What causes the createResource error to become undefined when it is refetched before being properly set?

Retrieving JSON data using Angular 2's HTTP GET request

How can I transfer information from one page to another in Next.js 14 without displaying the data in the URL?

Serious issue: a dependency request is an expression (Warning from Angular CLI)

search for a specific value within a nested subfield of an asterisk star field in Firestore

Numerous unspecified generic arguments

Issue with constructor including an interface

The "shape" property is not available while utilizing generics with toZod

Encountering a sign-in issue with credentials in next-auth. The credential authorization process is resulting in a

The 'items' property cannot be linked to 'virtual-scroller' as it is not a recognized attribute

`Changing environment variables in Angular during execution`

Challenges with importing VideoJs VR in Angular

What steps should I take to convert the lazyload module in routes into a regular module?

Discovering various kinds of data with a single generic type

I'm having trouble with the @Input() binding in my custom directive and it's not working as intended

The element 'filter' property cannot be found

My application is experiencing issues due to a malfunction when refreshing with query parameters in Angular 2

Tips for importing a file with a dynamic path in Angular 6