I'm doing migration from 0.5 to 1.0.
While reading, I notice 2 different way on declaring attributes, using hostAttributes and properties.
What are difference between those 2 ?
Host attributes are attributes that do not match to an element's corresponding Javascript property (which you declare in properties). This includes attributes like class, tabindex, data-* attributes, aria-roles, etc. To declare them during create-time, you must set them in the hostAttributes object. If you are going to bind values into them, you must use $= (which calls Element.setAttribute) rather than =.
Sources:
If a custom element needs HTML attributes set on it at create-time, the attributes may be declared in a hostAttributes property on the prototype, where keys are the attribute names and values are the values to be assigned.
But now since listeners and hostAttributes have been removed from element metadata
we can use _ensureAttribute as an alternative to define these kind of attributes
ex:-
this._ensureAttribute('tabindex', 0); you can declare all such properties in ready
来源：https://stackoverflow.com/questions/30723418/what-are-difference-between-hostattributes-and-properties-in-polymer