Added utils service with downloadFile() method

no issue

- pattern of downloading a file by creating an iframe and setting the `src` attribute was repeated throughout the codebase and was using a mix of native and jQuery patterns
- added a `utils` service for housing one-off utility methods like this to avoid repetition and mixed patterns becoming more widespread (we want to get rid of jQuery usage)

ghost/admin/app/controllers/members.js

@@ -33,6 +33,7 @@ export default class MembersController extends Controller {
     @service membersStats;
     @service router;
     @service store;
+    @service utils;
 
     queryParams = [
         'label',
@@ -265,15 +266,7 @@ export default class MembersController extends Controller {
         let downloadParams = new URLSearchParams(this.getApiQueryObject());
         downloadParams.set('limit', 'all');
 
-        let iframe = document.getElementById('iframeDownload');
+        this.utils.downloadFile(`${exportUrl}?${downloadParams.toString()}`);
-
-        if (!iframe) {
-            iframe = document.createElement('iframe');
-            iframe.id = 'iframeDownload';
-            iframe.style.display = 'none';
-            document.body.append(iframe);
-        }
-        iframe.setAttribute('src', `${exportUrl}?${downloadParams.toString()}`);
     }
 
     @action

ghost/admin/app/controllers/settings/labs.js

@@ -42,6 +42,7 @@ export default Controller.extend({
     notifications: service(),
     session: service(),
     settings: service(),
+    utils: service(),
 
     importErrors: null,
     importSuccessful: false,
@@ -140,14 +141,7 @@ export default Controller.extend({
         },
 
         downloadFile(endpoint) {
-            let downloadURL = this.get('ghostPaths.url').api(endpoint);
+            this.utils.downloadFile(this.ghostPaths.url.api(endpoint));
-            let iframe = $('#iframeDownload');
-
-            if (iframe.length === 0) {
-                iframe = $('<iframe>', {id: 'iframeDownload'}).hide().appendTo('body');
-            }
-
-            iframe.attr('src', downloadURL);
         },
 
         async saveOAuthSettings() {

ghost/admin/app/controllers/settings/theme.js

@@ -1,5 +1,4 @@
 /* eslint-disable ghost/ember/alias-model-in-controller */
-import $ from 'jquery';
 import Controller from '@ember/controller';
 import {computed} from '@ember/object';
 import {isEmpty} from '@ember/utils';
@@ -48,6 +47,7 @@ export default Controller.extend({
     notifications: service(),
     session: service(),
     settings: service(),
+    utils: service(),
 
     dirtyAttributes: false,
     newNavItem: null,
@@ -127,14 +127,7 @@ export default Controller.extend({
         },
 
         downloadTheme(theme) {
-            let downloadURL = `${this.get('ghostPaths.apiRoot')}/themes/${theme.name}/download/`;
+            this.utils.downloadFile(`${this.get('ghostPaths.apiRoot')}/themes/${theme.name}/download/`);
-            let iframe = $('#iframeDownload');
-
-            if (iframe.length === 0) {
-                iframe = $('<iframe>', {id: 'iframeDownload'}).hide().appendTo('body');
-            }
-
-            iframe.attr('src', downloadURL);
         },
 
         deleteTheme(theme) {

ghost/admin/app/controllers/staff/user.js

@@ -20,6 +20,7 @@ export default Controller.extend({
     notifications: service(),
     session: service(),
     slugGenerator: service(),
+    utils: service(),
 
     personalToken: null,
     limitErrorMessage: null,
@@ -381,18 +382,7 @@ export default Controller.extend({
     },
 
     _exportDb(filename) {
-        let exportUrl = this.get('ghostPaths.url').api('db');
+        this.utils.downloadFile(`${this.ghostPaths.url.api('db')}?filename=${filename}`);
-        let downloadURL = `${exportUrl}?filename=${filename}`;
-        let iframe = document.getElementById('iframeDownload');
-
-        if (!iframe) {
-            iframe = document.createElement('iframe');
-            iframe.id = 'iframeDownload';
-            iframe.style.display = 'none';
-            document.body.append(iframe);
-        }
-
-        iframe.setAttribute('src', downloadURL);
     },
 
     deleteUser: task(function *() {

ghost/admin/app/services/utils.js

@@ -0,0 +1,16 @@
+import Service from '@ember/service';
+
+export default class UtilsService extends Service {
+    downloadFile(url) {
+        let iframe = document.getElementById('iframeDownload');
+
+        if (!iframe) {
+            iframe = document.createElement('iframe');
+            iframe.id = 'iframeDownload';
+            iframe.style.display = 'none';
+            document.body.append(iframe);
+        }
+
+        iframe.setAttribute('src', url);
+    }
+}