An app is 'reactive' when the state and the UI automically stay synched. If the UI changes, the state will automatically update to reflect the change. If the state (data) changes, the UI will automatically update to reflect the change.
If you update the form, then the object on the right (the state) should update. If you update the properties of the object on the right, the form should update.
If you use vanilla js, it takes a lot of code to keep the state and the UI synched!