Storybook: Auto-set a 'STORYBOOK' environment variable to 'true'

[kripod]

Is your feature request related to a problem? Please describe.

When using different configuration for development, production and Storybook, it’s desirable to know whether we’re in a Storybook environment by querying process.env.STORYBOOK. For instance, a postcss.config.js file’s excerpt could look as follows:

module.exports = {
  plugins: {
    "postcss-import",
    "tailwindcss",
    "postcss-preset-env",

    // Simulate pseudos (only for Storybook)
    ...(process.env.STORYBOOK && { "postcss-pseudo-classes" })
}
  }
}

Describe the solution you'd like

Similarly to the convention of popular CI services, an environment variable for STORYBOOK should be set to true by default. It seems to blend well with Storybook’s existing env var handling mechanism.

Describe alternatives you've considered

Using cross-env for scripts defined in package.json. It’s error-prone and often forgotten by UNIX-only users who would prefer just STORYBOOK=true && start-storybook.

Are you able to assist bring the feature to reality?

No, unfortunately, I’m too busy at this time to familiarize myself with the codebase.

[kripod]

This is not stale.

[toshi1127]

@shilman
Can I try this?

[shilman]

Yo-ho-ho!! I just released https://github.com/storybookjs/storybook/releases/tag/v6.1.0-beta.3 containing PR #12997 that references this issue. Upgrade today to the @next NPM tag to try it out!

npx sb upgrade --prerelease

Closing this issue. Please re-open if you think there's still more to do.