AngularDart - Use Form Action
In Angular you would instead do the request in code, because form action="..." would reload the application or even another page which usually is not what you want in a single page application (SPA):
<form (ngSubmit)="onSubmit()"and then post the form in Dart code like shown in the question in Dart: AJAX form submit
I haven't done this myself in years and don't have a full example, but it should get you going.