based on https://jsfiddle.net/magic2/hLrT7/
invoke directive api from upper controller
test a Controller with $scope
test a Controller
test a Service
No-Library (pure JS), HTML, CSS, JavaScript
AngularJS 1.4.8, HTML, CSS, JavaScript
D3 3.x, HTML, CSS, JavaScript
use $watch in directive for primitives
ng-repeat: creates new scope