They also allow you to plug the inputs of one component into the outputs of another in a declarative way with model-driven views. So, if you have a menu that allows a user to choose a piece of data to work with, you can do something like this:

    <select id = 'menu'>
        <option />
        ...
    </select>
    <x-item-editor item_key = "{{ menu.value }}"/>

I haven't used the library yet, so I'm sure the syntax is wrong, but you can see how x-item-editor can know which item to edit by consuming the select's value property, without needing any glue in the JS.