NodeBind should support binding to events

[rafaelw]

Polymer supports this following kind of thing:

<div on-click="{{ myClickHandler }}"></div>

It does this at the polymer-expressions layer. I think this is very common behavior and should be a concern of element's NodeBind.

Here's how I propose this work:

HTMLElement allows binding to 'on-', by setting up a binding to the event whose name is the first N non-whitespace characters following 'on-'. The behavior of the binding is to

addEventListener(name, function(e) { 
  var fn = observable.getValue();
  if (typeof fn == 'function')
    fn(e);
  else
    console.warn('cannot invoke non-function: ' + fn);
});

One thing to note here is that the bindingValue doesn't really need to be an observer, even though it is dynamic. It's sufficient to retrieve the value when the event is handled.

Thus the implementation of the element that handles the binding might not call open(), but only getValue() on the observable.

[rafaelw]

Also, appropos:

Polymer/polymer#368 (comment)

[rafaelw]

Fixed: 5030c46