Write a preset addon

Storybook preset addons are grouped collections of babel, webpack, and addons configurations that support specific use cases in Storybook, such as TypeScript or MDX support.

This doc covers the presets API and how to use the presets mechanism for advanced configuration.

Presets API

A preset is a set of hooks that is called by Storybook on initialization and can override configurations for babel, webpack, addons, and entries.

Each configuration has a similar signature, accepting a base configuration object and options, as in this Webpack example:

export async function webpack(baseConfig, options) {
  // Modify or replace config. 
  // Mutating the original reference object can cause unexpected bugs,
  // so in this example we replace.
  const { module = {} } = baseConfig;
 
  return {
    ...baseConfig,
    module: {
      ...module,
      rules: [
        ...(module.rules || []),
        {
          /* some new loader */
        },
      ],
    },
  };
}

Babel

The babel functions babel, babelDefault, and managerBabel all configure babel in different ways.

All functions take a Babel configuration object as their argument and can modify it or return a new object.

For example, Storybook's Mihtril support uses plugins internally and here's how it configures babel:

import { TransformOptions } from '@babel/core';
 
export function babelDefault(config: TransformOptions) {
  return {
    ...config,
    plugins: [
      ...config.plugins,
      [require.resolve('@babel/plugin-transform-react-jsx'), {}, 'preset'],
    ],
  };
}

• babel is applied to the preview config, after it has been initialized by storybook
• babelDefault is applied to the preview config before any user presets have been applied
• managerBabel is applied to the manager.

Webpack

The Webpack functions webpack, webpackFinal, and managerWebpack configure Webpack.

All functions take a webpack4 configuration object.

For example, here is how Storybook automatically adopts create-react-app's configuration if it's installed, where applyCRAWebpackConfig is a set of smart heuristics for modifying the input config.

export function webpackFinal(config, { configDir }) {
  if (!isReactScriptsInstalled()) {
    logger.info('=> Using base config because react-scripts is not installed.');
    return config;
  }
 
  logger.info('=> Loading create-react-app config.');
  return applyCRAWebpackConfig(config, configDir);
}

• webpack is applied to the preview config after it has been initialized by Storybook
• webpackFinal is applied to the preview config after all user presets have been applied
• managerWebpack is applied to the manager config

As of Storybook 6.3, Storybook can run with either webpack4 or webpack5 builder. If your addon needs to know which version of Webpack it's running inside, the version and the actual Webpack instance itself are both available inside your preset:

export function webpackFinal(config, { presets }) {
  const version = await presets.apply('webpackVersion');
  const instance = (await presets.apply('webpackInstance'))?.default;
 
  logger.info(`=> Running in webpack ${version}: ${instance}`);
  return config;
}

Manager entries

The addon config managerEntries allows you to add addons to Storybook from within a preset. For addons that require custom Webpack/Babel configuration, it is easier to install the preset, and it will take care of everything.

For example, the Storysource preset contains the following code:

/* nothing needed */

This is equivalent to registering the addon manually in main.js:

module.exports = {
  managerEntries: ['some-storybook-addon/entry-point.js'],
};

Preview entries

The addon config function allows you to add extra preview configuration from within a preset, for example to add parameters or decorators from an addon.

For example, the Backgrounds preset contains the following code:

export function config(entry = []) {
  return [...entry, require.resolve('./defaultParameters')];
}

Which in turn invokes:

export const parameters = {
  backgrounds: {
    values: [
      { name: 'light', value: '#F8F8F8' },
      { name: 'dark', value: '#333333' },
    ],
  },
};

This is equivalent to exporting the backgrounds parameter manually in main.js.

Addons

For users, the name managerEntries might be a bit too technical, so instead both users and preset-authors can simply use the addons property:

module.exports = {
  addons: ['@storybook/addon-storysource'],
};

The array of values can support both references to other presets and addons that should be included into the manager.

Storybook will automatically detect whether a reference to an addon is a preset or a manager entry by checking if the package contains a ./preset.js or ./register.js (manager entry), falling back to preset if it is unsure.

If this heuristic is incorrect for an addon you are using, you can explicitly opt in to an entry being an a manager entry using the managerEntries key.

Here's what it looks when combining presets and manager entries in the addons property:

module.exports = {
  addons: [
    '@storybook/addon-docs/preset', // A preset registered here, in this case from the addon-docs addon.
  ],
};

Entries

Entries are the place to register entry points for the preview. For example it could be used to make a basic configure-storybook preset that loads all the *.stories.js files into SB, instead of forcing people to copy-paste the same thing everywhere.

Advanced Configuration

The presets API is also more powerful than the standard configuration options available in Storybook, so it's also possible to use presets for more advanced configuration without actually publishing a preset yourself.

For example, some users want to configure the Webpack for Storybook's UI and addons (issue), but this is not possible using standard Webpack configuration (it used to be possible before SB4.1). However, you can achieve this with a private preset.

If it doesn't exist yet, create a file .storybook/main.js:

module.exports = {
  managerWebpack: async (config, options) => {
    // update config here
    return config;
  },
  managerBabel: async (config, options) => {
    // update config here
    return config;
  },
  webpackFinal: async (config, options) => {
    // change webpack config
    return config;
  },
  babel: async (config, options) => {
    return config;
  },
};

Preview/Manager templates

It's also possible to programmatically modify the preview head/body HTML using a preset, similar to the way preview-head.html/preview-body.html can be used to configure story rendering. The previewHead and previewBody functions accept a string, which is the existing head/body, and return a modified string.

For example, the following snippet adds a style tag to the preview head programmatically:

module.exports = {
  previewHead: (head) => (`
    ${head}
    <style>
      #main {
        background-color: yellow;
      }
    </style>
  `);
};

Similarly, the managerHead can be used to modify the surrounding "manager" UI, analogous to manager-head.html.

Finally, the preview's main page template can also be overridden using the previewMainTemplate, which should return a reference to a file containing an .ejs template that gets interpolated with some environment variables. For an example, see the Storybook's default template.

Sharing advanced configuration

Change your main.js file to:

const path = require('path');
 
module.exports = {
  addons: [path.resolve('./.storybook/my-preset')],
};

and extract the configuration to a new file ./storybook/my-preset.js:

module.exports = {
  managerWebpack: async (config, options) => {
    // Update config here
    return config;
  },
  managerBabel: async (config, options) => {
    // Update config here
    return config;
  },
  webpackFinal: async (config, options) => {
    return config;
  },
  babel: async (config, options) => {
    return config;
  },
};

Place your my-preset.js file wherever you want, if you want to share it far and wide you'll want to make it its own package.