Use promise syntax with Helper.getContent

Fix
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/12198#note_37143217

app/assets/javascripts/repo/components/repo_sidebar.vue

@@ -42,19 +42,20 @@ const RepoSidebar = {
         file.loading = false;
       } else {
         Service.url = file.url;
-        // I need to refactor this to do the `then` here.
-        // Not a callback. For now this is good enough.
-        // it works.
-        Helper.getContent(file, () => {
+        Helper.getContent(file)
+          .then(() => {
             file.loading = false;
             Helper.scrollTabsRight();
-        });
+          })
+          .catch(Helper.loadingError);
       }
     },
 
     goToPreviousDirectoryClicked(prevURL) {
       Service.url = prevURL;
-      Helper.getContent(null, () => Helper.scrollTabsRight());
+      Helper.getContent(null)
+        .then(() => Helper.scrollTabsRight())
+        .catch(Helper.loadingError);
     },
   },
 };

app/assets/javascripts/repo/helpers/repo_helper.js

@@ -135,14 +135,13 @@ const RepoHelper = {
     return isRoot;
   },
 
-  getContent(treeOrFile, cb) {
+  getContent(treeOrFile) {
     let file = treeOrFile;
     // const loadingData = RepoHelper.setLoading(true);
     return Service.getContent()
     .then((response) => {
       const data = response.data;
       // RepoHelper.setLoading(false, loadingData);
-      if (cb) cb();
       Store.isTree = RepoHelper.isTree(data);
       if (!Store.isTree) {
         if (!file) file = data;

spec/javascripts/repo/components/repo_sidebar_spec.js

@@ -64,9 +64,10 @@ describe('RepoSidebar', () => {
   describe('methods', () => {
     describe('fileClicked', () => {
       it('should fetch data for new file', () => {
-        spyOn(Helper, 'getContent');
+        spyOn(Helper, 'getContent').and.callThrough();
         const file1 = {
           id: 0,
+          url: '',
         };
         RepoStore.files = [file1];
         RepoStore.isRoot = true;
@@ -74,7 +75,7 @@ describe('RepoSidebar', () => {
 
         vm.fileClicked(file1);
 
-        expect(Helper.getContent).toHaveBeenCalledWith(file1, jasmine.any(Function));
+        expect(Helper.getContent).toHaveBeenCalledWith(file1);
       });
 
       it('should hide files in directory if already open', () => {