docs: update example config for TypeScript compatibility

[blimmer]

The example config specified in the README:

// .storybook/main.js

const turbosnap = require('vite-plugin-turbosnap');

module.exports = {
  core: { builder: '@storybook/builder-vite' },
  async viteFinal(config, { configType }) {
    // Turbosnap is only useful when building for production
    if (configType === 'PRODUCTION') {
      config.plugins.push(turbosnap({ rootDir: config.root }));
    }

    // ...And any other config you need to change...

    // return the customized config
    return config;
  },
}

Produces errors in a .storybook/main.ts file.

1. config.plugins is possibly undefined.
2. config.root is possibly undefined.

This PR updates the example to be compatible with JS and TS.

[IanVS]

Thanks, @blimmer. This is actually what I do myself, what do you think of it?

import type { ViteFinal } from '@storybook/builder-vite';
import { mergeConfig } from 'vite';
import turbosnap from 'vite-plugin-turbosnap';

export const viteFinal: ViteFinal = async (config, { configType }) => {
  return mergeConfig(config, {
    plugins: configType === 'PRODUCTION' ? [turbosnap({ rootDir: config.root ?? process.cwd() })] : [],
  });
};

[blimmer]

Ah, sure, since mergeConfig does a deep merge already, that seems reasonable. process.cwd() also seems like a reasonable fallback (I think that, in practice, it's pretty much always set anyway...).

I'll update the PR!

[IanVS]

Great, thanks!