[Ruphin]

Two-way data binding is indeed a bad pattern, but the issue is that there is only syntax to bind data down, with [[]]. Sometimes it makes sense to get data from a child, and {{}} can be convenient, as long as you follow the rule that you only use it to retrieve data, and never try to set it. Unfortunately there is no syntax for such a binding, but as long as you follow the style that {{}} is only used as a one-way binding (but in the opposite direction compared to [[]]) it works just fine.

I usually create elements that are responsible for managing a certain type of data, and expose is through properties. This data can then be used anywhere in the application, by using that element and observing with {{}}. I really like that pattern, it feels like a traditional model object that exposes a nice API to consumers.

I definitely agree that you need a pretty strict style guide, it's too easy to go crazy and just stitch things together, and end up with an entangled mess.