Move the props declaration to the script

[danieldietrich]

Currently we define default values. It would be better to define types.

props: {
  selected: Boolean,
  index: Number
}

One challenge is to evaluate the script before defining the custom class because the prop names are needed for these static observedAttributes method.

[danieldietrich]

After thinking about it, we should leave it, as-is.

Vue for example needs a props type definitions and a script which returns a data function, which in turn return the prop values. That is quite a bit.

Candid just defines the props (= observed attributes), which combine initial values and therefore types. That is simpler than the approach of Vue.