Fixes #877

Throw on adding a global decorator after stories have already been added. The global decorator will not be applied.

app/react/src/client/preview/client_api.js

@@ -8,6 +8,7 @@ export default class ClientApi {
     this._storyStore = storyStore;
     this._addons = {};
     this._globalDecorators = [];
+    this._storiesAdded = false;
   }
 
   setAddon(addon) {
@@ -18,6 +19,9 @@ export default class ClientApi {
   }
 
   addDecorator(decorator) {
+    if (this._storiesAdded) {
+      throw new Error('Global decorators added after loading stories will not be applied');
+    }
     this._globalDecorators.push(decorator);
   }
 
@@ -51,6 +55,8 @@ export default class ClientApi {
     });
 
     api.add = (storyName, getStory) => {
+      this._storiesAdded = true;
+
       if (typeof storyName !== 'string') {
         throw new Error(`Invalid or missing storyName provided for a "${kind}" story.`);
       }

app/react/src/client/preview/client_api.test.js

@@ -150,6 +150,16 @@ describe('preview.client_api', () => {
       expect(storyStore.stories[0].fn()).toBe('bb-Hello');
     });
 
+    it('should throw on adding global decorators after stories', () => {
+      const storyStore = new StoryStore();
+      const api = new ClientAPI({ storyStore });
+      const localApi = api.storiesOf('none');
+      localApi.add('storyName', () => 'Hello');
+      expect(() => {
+        api.addDecorator(fn => `bb-${fn()}`);
+      }).toThrow('Global decorators added after loading stories will not be applied');
+    });
+
     it('should utilize both decorators at once', () => {
       const storyStore = new StoryStore();
       const api = new ClientAPI({ storyStore });