Form Validation - Vue

I am looking thru the doc and it seems very obscure how to deal with form validation. Of course, I found this:
https://ionicthemes.com/tutorials/about/forms-and-validation-in-ionic . But I am using Vue.

I assumed I would find some basic «how to». For example, the doc for <ion-item> stipulates that « Items containing an input will highlight the bottom border of the input with a different color when focused, valid, or invalid».

My question is more: How can we set the ion-item to invalid?

For now, all I see is that Ionic is still tightly coupled with Angular.

Any thoughts?

here is an example where i used a 3rd party plugin for validation in vue with ionic.