storybook/docs/_snippets/storybook-main-using-existing-config.md

import custom from '../webpack.config.js'; // 👈 Custom Webpack configuration being imported.

export default {
  // Replace your-framework with the framework you are using (e.g., react-webpack5, vue3-vite)
  framework: '@storybook/your-framework',
  stories: ['../src/**/*.mdx', '../src/**/*.stories.@(js|jsx|mjs|ts|tsx)'],
  webpackFinal: async (config) => {
    return {
      ...config,
      module: { ...config.module, rules: [...config.module.rules, ...custom.module.rules] },
    };
  },
};

// Replace your-framework with the framework you are using (e.g., react-webpack5, vue3-vite)
import type { StorybookConfig } from '@storybook/your-framework';

import custom from '../webpack.config.js'; // 👈 Custom Webpack configuration being imported.

const config: StorybookConfig = {
  framework: '@storybook/your-framework',
  stories: ['../src/**/*.mdx', '../src/**/*.stories.@(js|jsx|mjs|ts|tsx)'],
  webpackFinal: async (config) => {
    return {
      ...config,
      module: { ...config.module, rules: [...config.module.rules, ...custom.module.rules] },
    };
  },
};

export default config;