Lightweight Declarative Binding

[Michael Bleigh]

I've been thinking through how it might be possible to get some of the common advantages of template binding without the need to do full-scale MDV. This would have advantages for performance reasons, but would also in my opinion help address the "App Root Element" issue that I keep running into building my Polymer apps (wherein the entire application is absorbed into a containing element for the sole purpose of getting template binding semantics). Basically, it would introduce one to three new "magic attribute prefixes" similar to the on-* event binding. It would work something like this:

<core-ajax bind-response="usercard" url="/users/abc" handleAs="json"></core-ajax>
<user-card id="usercard"></user-card>

Presuming that the user-card element is something that accepts a "model" property with user data and displays something useful. The bind-* prefix would work in a two-way fashion similar to current mustache binding, where everything after the "bind-" is considered the attribute or property name to bind. There could also be pub-* and sub-* to exclusively publish or exclusively subscribe to a value.

The value of the magic attributes would be the id of an element in the same document context as the bound element (i.e. retrieved using this.ownerDocument.getElementById). This way shadow boundaries would be respected and utilized appropriately. By default the "model" property would be set on the target element; however, you could easily have a syntax like "usercard.data" where a period denotes the separation between the DOM id and the property name.

This paradigm would solve the most common use cases I run into when wanting to declaratively bind. It does *not* solve things like repeating templates or things that can't have an id or a knowable-in-advance id for some reason. What I like about it is that I can use these attributes completely outside of Polymer's template binding setup.

Not sure that this is perfect, but throwing it out for discussion after thinking on it over the weekend.

[Rob Dodson]

RE: the "app root element", I tend to put the guts of my app in an auto-binding template (see here) and then use that as the starting point for my app. It doesn't solve the performance problems associated with MDV but hopefully 0.8 addresses some of those issues.

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