angularjs - Angular: Using $scope vs calling a controller attribute -

i've been reading ng-book , worked through code school angular course other day , confused when use $scope in controller , when use attribute of controller.

in code school course, controllers setup this:

app.controller('librarycontroller', function(){   this.books = getbooks //some function gets array }); 

but in ng-book , elsewhere, i've seen done scope:

app.controller('librarycontroller', function($scope){   $scope.books = getbooks //some function gets array }) 

from can tell, these 2 approaches same. first used in view this:

<div ng-controller="librarycontroller libraryctrl">   <ul>     <li ng-repeat="book in libraryctrl.books"> 

while second be

<div ng-controller="librarycontroller">   <ul>     <li ng-repeat="book in books"> 

am not understanding fundamental here? there difference in these 2 approaches , why $scope approach used exclusively?

i see 2 reasons why scope approach used more controller as approach:

1. the scope approach 1 has been existing long time. it's since version 1.2 (iirc) "controller as" syntax introduced. people got used traditional way, example written way.
2. the handling of this in javascript nightmare (imho). have read documentation of ever callback function used make sure this doesn't change when callback called. using scope doesn't have problem.