```js
// MyComponent.stories.js

import React from 'react';
import { INITIAL_VIEWPORTS } from '@storybook/addon-viewport';

export default {
  title: 'Stories',
  parameters: {
    // the viewports object from the Essentials addon
    viewport: {
      // the viewports you want to use
      viewports: INITIAL_VIEWPORTS,
      // your own default viewport
      defaultViewport: 'iphone6'
    },
  };
};

export const MyStory = () => <div />;
MyStory.parameters = {
  viewport: {
    defaultViewport: 'iphonex'
  },
};
```
