Standardize access to CSRF token in JavaScript

app/assets/javascripts/blob/blob_file_dropzone.js

@@ -3,6 +3,7 @@
 
 import '../lib/utils/url_utility';
 import { HIDDEN_CLASS } from '../lib/utils/constants';
+import csrf from '../lib/utils/csrf';
 
 function toggleLoading($el, $icon, loading) {
   if (loading) {
@@ -36,9 +37,7 @@ export default class BlobFileDropzone {
       maxFiles: 1,
       addRemoveLinks: true,
       previewsContainer: '.dropzone-previews',
-      headers: {
-        'X-CSRF-Token': $('meta[name="csrf-token"]').attr('content'),
-      },
+      headers: csrf.headers,
       init: function () {
         this.on('addedfile', function () {
           toggleLoading(submitButton, submitButtonLoadingIcon, false);

app/assets/javascripts/dropzone_input.js

@@ -2,6 +2,7 @@
 /* global Dropzone */
 import _ from 'underscore';
 import './preview_markdown';
+import csrf from './lib/utils/csrf';
 
 window.DropzoneInput = (function() {
   function DropzoneInput(form) {
@@ -50,9 +51,7 @@ window.DropzoneInput = (function() {
       paramName: 'file',
       maxFilesize: maxFileSize,
       uploadMultiple: false,
-      headers: {
-        'X-CSRF-Token': $('meta[name="csrf-token"]').attr('content')
-      },
+      headers: csrf.headers,
       previewContainer: false,
       processing: function() {
         return $('.div-dropzone-alert').alert('close');
@@ -260,9 +259,7 @@ window.DropzoneInput = (function() {
         dataType: 'json',
         processData: false,
         contentType: false,
-        headers: {
-          'X-CSRF-Token': $('meta[name="csrf-token"]').attr('content')
-        },
+        headers: csrf.headers,
         beforeSend: function() {
           showSpinner();
           return closeAlertMessage();

app/assets/javascripts/lib/utils/csrf.js

+/*
+This module provides easy access to the CSRF token and caches
+it for re-use. It also exposes some values commonly used in relation
+to the CSRF token (header key and headers object).
+
+If you need to refresh the csrfToken for some reason, just call `init` and
+then use the accessors as you would normally.
+
+If you need to compose a headers object, use the spread operator:
+
+```
+  headers: {
+    ...csrf.headers,
+    someOtherHeader: '12345',
+  }
+```
+ */
+
+const csrf = {
+  init() {
+    const tokenEl = document.querySelector('meta[name=csrf-token]');
+
+    if (tokenEl !== null) {
+      this.csrfToken = tokenEl.getAttribute('content');
+    } else {
+      this.csrfToken = null;
+    }
+  },
+
+  get token() {
+    return this.csrfToken;
+  },
+
+  get headerKey() {
+    return 'X-CSRF-Token';
+  },
+
+  get headers() {
+    if (this.csrfToken !== null) {
+      return {
+        [this.headerKey]: this.token,
+      };
+    }
+    return {};
+  },
+};
+
+csrf.init();
+
+// use our cached token for any $.rails-generated AJAX requests
+if ($.rails) {
+  $.rails.csrfToken = () => csrf.token;
+}
+
+export default csrf;
+

app/assets/javascripts/vue_shared/vue_resource_interceptor.js

 import Vue from 'vue';
 import VueResource from 'vue-resource';
+import csrf from '../lib/utils/csrf';
 
 Vue.use(VueResource);
 
@@ -18,9 +19,7 @@ Vue.http.interceptors.push((request, next) => {
 // New Vue Resource version uses Headers, we are expecting a plain object to render pagination
 // and polling.
 Vue.http.interceptors.push((request, next) => {
-  if ($.rails) {
-    request.headers.set('X-CSRF-Token', $.rails.csrfToken());
-  }
+  request.headers.set(csrf.headerKey, csrf.token);
 
   next((response) => {
     // Headers object has a `forEach` property that iterates through all values.

spec/javascripts/lib/utils/csrf_token_spec.js

+import csrf from '~/lib/utils/csrf';
+
+describe('csrf', () => {
+  beforeEach(() => {
+    this.tokenKey = 'X-CSRF-Token';
+    this.token = 'pH1cvjnP9grx2oKlhWEDvUZnJ8x2eXsIs1qzyHkF3DugSG5yTxR76CWeEZRhML2D1IeVB7NEW0t5l/axE4iJpQ==';
+  });
+
+  it('returns the correct headerKey', () => {
+    expect(csrf.headerKey).toBe(this.tokenKey);
+  });
+
+  describe('when csrf token is in the DOM', () => {
+    beforeEach(() => {
+      setFixtures(`
+        <meta name="csrf-token" content="${this.token}">
+      `);
+
+      csrf.init();
+    });
+
+    it('returns the csrf token', () => {
+      expect(csrf.token).toBe(this.token);
+    });
+
+    it('returns the csrf headers object', () => {
+      expect(csrf.headers[this.tokenKey]).toBe(this.token);
+    });
+  });
+
+  describe('when csrf token is not in the DOM', () => {
+    beforeEach(() => {
+      setFixtures(`
+        <meta name="some-other-token">
+      `);
+
+      csrf.init();
+    });
+
+    it('returns null for token', () => {
+      expect(csrf.token).toBeNull();
+    });
+
+    it('returns empty object for headers', () => {
+      expect(typeof csrf.headers).toBe('object');
+      expect(Object.keys(csrf.headers).length).toBe(0);
+    });
+  });
+});