On initialization, properties 'items' and 'selected' may be applied to an iron-selectable element in any order, by Polymer's _applyConfig method (code). If 'selected' is applied before 'items', a nullref occurs due to the _updateSelected observer.
This actually was indicative of a deeper problem in my BUILD. Elements were registering out of order, which broke data binding, which indirectly broke initialization.
Description
On initialization, properties 'items' and 'selected' may be applied to an iron-selectable element in any order, by Polymer's _applyConfig method (code). If 'selected' is applied before 'items', a nullref occurs due to the _updateSelected observer.
Expected outcome
No nullref.
Actual outcome
Stack trace:
Live Demo
This is a failed attempt at repro (can't control property iteration order): http://jsbin.com/nafofokofe/edit?html,js,output
Steps to reproduce
Use an iron-pages element with a "selected" binding.
Browsers Affected
All?
I have a 2-line fix ready, will supply it shortly.