REMOVE previously deprecated default export from backgrounds

MIGRATION.md

@@ -5,6 +5,8 @@
   - [Story hierarchy defaults](#story-hierarchy-defaults)
   - [Options addon deprecated](#options-addon-deprecated)
   - [Individual story decorators](#individual-story-decorators)
+  - [Addon backgrounds uses parameters](#addon-backgrounds-uses-parameters)
+  - [Addon viewport uses parameters](#addon-backgrounds-uses-parameters)
 - [From version 4.0.x to 4.1.x](#from-version-40x-to-41x)
   - [Private addon config](#private-addon-config)
   - [React 15.x](#react-15x)
@@ -163,6 +165,25 @@ storiesOf('Stories', module)
   .add('centered', () => 'Hello', { decorators: [centered] });
 ```
 
+## Addon backgrounds uses parameters
+
+Similarly, `@storybook/addon-backgrounds` uses parameters to pass background options. If you previously had:
+
+```js
+import { withBackgrounds } from `@storybook/addon-backgrounds`;
+
+storiesOf('Stories', module)
+  .addDecorator(withBackgrounds(options));
+```
+
+You should replace it with:
+
+```js
+storiesOf('Stories', module).addParameters({ backgrounds: options });
+```
+
+You can pass `backgrounds` parameters at the global level (via `addParameters` imported from `@storybook/react` et al.), and the story level (via the third argument to `.add()`).
+
 ## Addon viewport uses parameters
 
 Similarly, `@storybook/addon-viewport` uses parameters to pass viewport options. If you previously had:
@@ -173,7 +194,7 @@ import { configureViewport } from `@storybook/addon-viewport`;
 configureViewport(options);
 ```
 
-You can replace it with:
+You should replace it with:
 
 ```js
 import { addParameters } from '@storybook/react'; // or others
@@ -214,17 +235,19 @@ However, if you're developing React components, this means you need to upgrade t
 Also, here's the error you'll get if you're running an older version of React:
 
 ```
+
 core.browser.esm.js:15 Uncaught TypeError: Object(...) is not a function
   at Module../node_modules/@emotion/core/dist/core.browser.esm.js (core.browser.esm.js:15)
-  at **webpack_require** (bootstrap:724)
+  at __webpack_require__ (bootstrap:724)
   at fn (bootstrap:101)
   at Module../node_modules/@emotion/styled-base/dist/styled-base.browser.esm.js (styled-base.browser.esm.js:1)
-  at **webpack_require** (bootstrap:724)
+  at __webpack_require__ (bootstrap:724)
   at fn (bootstrap:101)
   at Module../node_modules/@emotion/styled/dist/styled.esm.js (styled.esm.js:1)
-  at **webpack_require** (bootstrap:724)
+  at __webpack_require__ (bootstrap:724)
   at fn (bootstrap:101)
   at Object../node_modules/@storybook/components/dist/navigation/MenuLink.js (MenuLink.js:12)
+
 ```
 
 ### Generic addons

addons/backgrounds/src/constants.ts

@@ -1,7 +1,2 @@
 export const ADDON_ID = 'storybook/background';
 export const PARAM_KEY = 'backgrounds';
-
-export const EVENTS = {
-  SET: `${ADDON_ID}:set`,
-  UNSET: `${ADDON_ID}:unset`,
-};

addons/backgrounds/src/index.ts

@@ -1,43 +1,18 @@
-import { addons, makeDecorator, StoryContext, StoryGetter, WrapperSettings } from '@storybook/addons';
+import { makeDecorator, StoryContext, StoryGetter } from '@storybook/addons';
 import deprecate from 'util-deprecate';
 
-import { REGISTER_SUBSCRIPTION } from '@storybook/core-events';
-import { EVENTS } from './constants';
-import { BackgroundConfig } from './models';
-
-let prevBackgrounds: BackgroundConfig[];
-
-const subscription = () => () => {
-  prevBackgrounds = null;
-  addons.getChannel().emit(EVENTS.UNSET);
-};
-
-export const withBackgrounds = makeDecorator({
-  name: 'withBackgrounds',
-  parameterName: 'backgrounds',
-  skipIfNoParametersOrOptions: true,
-  allowDeprecatedUsage: true,
-  wrapper: (getStory: StoryGetter, context: StoryContext, { options, parameters }: WrapperSettings) => {
-    const data = parameters || options || [];
-    const backgrounds = Array.isArray(data) ? data : Object.values(data);
-
-    if (backgrounds.length === 0) {
+// This decorator is kept purely so we produce a decorator that is compatible with both
+// `addDecorator(withBackgrounds(...))` and `addDecorator(withBackgrounds)`
+export const withBackgrounds = deprecate(
+  makeDecorator({
+    name: 'withBackgrounds',
+    parameterName: 'backgrounds',
+    wrapper: (getStory: StoryGetter, context: StoryContext) => {
       return getStory(context);
-    }
-
-    if (prevBackgrounds !== backgrounds) {
-      addons.getChannel().emit(EVENTS.SET, backgrounds);
-      prevBackgrounds = backgrounds;
-    }
-    addons.getChannel().emit(REGISTER_SUBSCRIPTION, subscription);
-
-    return getStory(context);
-  },
-});
-
-export default deprecate(
-  withBackgrounds,
-  'The default export of @storybook/addon-backgrounds is deprecated, please `import { withBackgrounds }` instead'
+    },
+  }),
+  `Note that withBackgrounds(options) has been replaced by addParameters({ backgrounds: options})
+Read more about it in the migration guide: https://github.com/storybooks/storybook/blob/master/MIGRATION.md`
 );
 
 if (module && module.hot && module.hot.decline) {