```js
// MyComponent.stories.js

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 = () => ({
  template: '<div />',
});
myStory.parameters = {
  viewport: {
    defaultViewport: 'iphonex',
  },
};
```