State objects cannot be classes

[christopherthielen]

In angular-ui-router 0.x you could create a class for a state:

class ModalState implements StateDeclaration {
  constructor(def) {
    Object.assign(this, def);
  }
  onEnter() {
    this.modalInstance = $uibModal.open(...);
    thos.modalInstance.result.then(this.onClose.bind(this), this.onDismiss.bind(this));
  }
}

This worked fine back then because the internal State object's prototype was the user supplied StateDeclaration, i.e,

var internalState = Object.create(stateDeclaration)`

but this is no longer possible because we now use new State() to get the State (class) prototype, i.e.,

var internalState = Object.assign(new State(), stateDeclaration);

Since Object.assign only makes copies of the stateDeclaration's own properties, it does not make copies of the prototype onEnter function, for example.

---

We should switch back to the old behavior (internal state object's prototype is the user supplied state declaration). We will lose the ability to do obj instanceof State, but that is a small price to enable numerous other convenient features.

For example, hook functions can check for user-supplied state properties without explicitly querying state.self.property:

transitionService.onStart({ to: state => state.customflag }, ...)

Projects like sticky states can define new callbacks (like onInactivate) without also creating a statebuilder to enable access to the stateDeclaration.onInactivate property.