Replace $.get in single file diff with axios

app/assets/javascripts/single_file_diff.js

 /* eslint-disable func-names, prefer-arrow-callback, space-before-function-paren, no-var, prefer-rest-params, wrap-iife, one-var, one-var-declaration-per-line, consistent-return, no-param-reassign, max-len */
 
+import { __ } from './locale';
+import axios from './lib/utils/axios_utils';
+import createFlash from './flash';
 import FilesCommentButton from './files_comment_button';
 import imageDiffHelper from './image_diff/helpers/index';
 import syntaxHighlight from './syntax_highlight';
@@ -60,30 +63,31 @@ export default class SingleFileDiff {
   getContentHTML(cb) {
     this.collapsedContent.hide();
     this.loadingContent.show();
-    $.get(this.diffForPath, (function(_this) {
-      return function(data) {
-        _this.loadingContent.hide();
+
+    axios.get(this.diffForPath)
+      .then(({ data }) => {
+        this.loadingContent.hide();
         if (data.html) {
-          _this.content = $(data.html);
-          syntaxHighlight(_this.content);
+          this.content = $(data.html);
+          syntaxHighlight(this.content);
         } else {
-          _this.hasError = true;
-          _this.content = $(ERROR_HTML);
+          this.hasError = true;
+          this.content = $(ERROR_HTML);
         }
-        _this.collapsedContent.after(_this.content);
+        this.collapsedContent.after(this.content);
 
         if (typeof gl.diffNotesCompileComponents !== 'undefined') {
           gl.diffNotesCompileComponents();
         }
 
-        const $file = $(_this.file);
+        const $file = $(this.file);
         FilesCommentButton.init($file);
 
         const canCreateNote = $file.closest('.files').is('[data-can-create-note]');
         imageDiffHelper.initImageDiff($file[0], canCreateNote);
 
         if (cb) cb();
-      };
-    })(this));
+      })
+      .catch(createFlash(__('An error occurred while retrieving diff')));
   }
 }

spec/features/expand_collapse_diffs_spec.rb

@@ -112,13 +112,6 @@ feature 'Expand and collapse diffs', :js do
         wait_for_requests
       end
 
-      it 'makes a request to get the content' do
-        ajax_uris = evaluate_script('ajaxUris')
-
-        expect(ajax_uris).not_to be_empty
-        expect(ajax_uris.first).to include('large_diff.md')
-      end
-
       it 'shows the diff content' do
         expect(large_diff).to have_selector('.code')
         expect(large_diff).not_to have_selector('.nothing-here-block')