AngularJS：如何更新$ scope属性

I have an object on the $scope that dictates the "next screen" for the app to go after update (I'm in a wizard-like multi-screen new form) and as each screen is displayed, I want to show the current and all subsequent screens in the sidebar -- easy to go back for the user to make changes but not allowing him/her to skip steps by not displaying future screens.I have an object on the $scope that dictates th