Angular 4 Form still valid if not allowed value inserted

Question

In my angular 4 project I have multiple forms, some of these forms have an input field that needs to be controlled, and if the value isn't correct the button save needs to be disabled.

If i want a input field with only positive numbers I use this:

<input type="number" class="form-control" id="blockFrom" required  
[(ngModel)]="blockFrom" min="0" name="blockFrom">

<button (click)="save()" [disabled]="modelForm.form.invalid || 
modelForm.form.pristine">save</button>

But if I write in the input field negative numbers the button is enabled (I see the input field red correctly because the value isn't permitted) Why? How can I block the button if value is negative?

Answer 1

You can put a function directly here: [disabled]="checkIfValid()".

The function will then checks your form data.

it should look like this:

checkIfValid():boolean
{
 return blockForm>0
}