Wrap in IIFE and add "use strict" statement

app/app.js

@@ -1,49 +1,57 @@
 /*global angular */
 
-angular.module("youtube-thumbnail-preview", ["ngFilemodel"])
-
-.controller("main", ["$scope", function ($scope) {
-
-    /** Stores info about the fake video that is displayed. */
-    $scope.info = {
-        title: "Title of the video",
-        uploader: "Channel Name",
-        time: "12:34",
-        uploadtime: "42 minutes ago",
-        views: "123,456",
-    };
-
-    /** FileList model for the thumbnail selection */
-    $scope.imageFiles = null;
-    /** The currently displayed data URL */
-    $scope.image = null;
-
-    /**
-     * Reads the given File object as a data URL and stores it in $scope.image.
-     */
-    function loadFile(file) {
-        var reader = new FileReader();
-        reader.onload = function (event) {
-            $scope.$apply(function () {
-                $scope.image = event.target.result;
-            });
+(function (angular) {
+    "use strict";
+
+    // -- MODULE DECLARATION
+    angular.module("youtube-thumbnail-preview", ["ngFilemodel"])
+
+    // MAIN CONTROLLER
+    .controller("main", ["$scope", function ($scope) {
+
+        /** Stores info about the fake video that is displayed. */
+        $scope.info = {
+            title: "Title of the video",
+            uploader: "Channel Name",
+            time: "12:34",
+            uploadtime: "42 minutes ago",
+            views: "123,456",
         };
-        reader.readAsDataURL(file);
-    }
 
-    // load thumbnail on file selection
-    $scope.$watchCollection("imageFiles", function (files) {
-        if (files && files.length) {
-            loadFile(files[0]);
+        /** FileList model for the thumbnail selection */
+        $scope.imageFiles = null;
+        /** The currently displayed data URL */
+        $scope.image = null;
+
+        /**
+         * Reads the given File as a data URL and stores it in $scope.image.
+         */
+        function loadFile(file) {
+            var reader = new FileReader();
+            reader.onload = function (event) {
+                $scope.$apply(function () {
+                    $scope.image = event.target.result;
+                });
+            };
+            reader.readAsDataURL(file);
         }
-    });
 
-}])
+        // load thumbnail on file selection
+        $scope.$watchCollection("imageFiles", function (files) {
+            if (files && files.length) {
+                loadFile(files[0]);
+            }
+        });
+
+    }])
+
+    // THUMBNAIL DIRECTIVE
+    .directive("appThumbnail", [function () {
+        return {
+            restrict: "E",
+            scope: true,
+            templateUrl: "app/thumbnail.html",
+        };
+    }]);
 
-.directive("appThumbnail", [function () {
-    return {
-        restrict: "E",
-        scope: true,
-        templateUrl: "app/thumbnail.html",
-    };
-}]);
+})(angular);