Consider providing a mechanism to easily observe a set of property paths

[sorvell]

It's common to want pass object data to a custom element and want to react to changes in some set of paths in that object. We should consider adding a mechanism to make this pattern easy to implement.

It might look like this:

observers: {
  'obj.name.first obj.name.last': 'nameChanged'
}

and this would mean, whenever this.obj.name.first|last changes, the nameChanged method should be called.

[morethanreal]

How about inverting the key-value of the dictionary, ie. 'nameChanged': ['obj.name.first', 'obj.name.last'] etc? The list of paths to observe could get quite long. One example would be the various animation properties in g-animation. It would also make it easier to inherit.

[aeosynth]

you may want to look at rfc 6901:

JSON Pointer defines a string syntax for identifying a specific value
within a JavaScript Object Notation (JSON) document.

it uses slashes instead of dots as separators

[sorvell]

Fixed via merging CompoundPathObserver branch, fea8c48.

We added an observe block where custom change handlers can be specified. This has a number of advantages. You can use the change handler names you want. If multiple properties are registered to fire the same change handler, it will only fire once if any of the set of properties changes 'at the same time', and it's possible to observe subpaths (a.b.c). For example,

observe: {
  foo: 'invalidate',
  bar: 'invalidate',
  'a.b.c': 'subPathChanged'
},
invalidate: function() { ... },
subPathChanged() { ... },