`$app/environment.browser` isn't reliable for libraries (packaging)

Describe the bug

Every Svelte UI library that want to check if the current environment is the server or the client, uses often the variable $app/environment.browser. While it’s the recommended way for SvelteKit normal application, this is problematic when the library do svelte-kit package, to get the library compiled output.

Any project using a UI library that written in SvelteKit, exported via svelte-kit package, and use the browser variable, will fail to be used in Svelte projects that are outside the SvelteKit environment (e.g. in REPL), since the output still use the browser variable, and wait for the environment to compile it.

There are two possible solutions:

1. Put the browser variable as part of the specific Svelte environment, instead of the specific SvelteKit environment. (Recommended)
2. When compiled via svelte-kit package, define the value of browser to be equal to typeof window !== 'undefined'.

Sadly, I’ve seen too many libraries do this mistake, and proposed them to use typeof window !== 'undefined' instead. However, the logic and the sanity are on their side 😃

Reproduction

Just use the browser definition, export via svelte-kit package and see the output isn’t compiled at all, the browser stays in the output.

Logs

No response

System Info

N/A

Severity

annoyance

Additional Information

No response

[TorstenDittmann]

Not sure if related, but after upgrading to kit version next.409, I’ve been running into following issues with vitetest.

[benmccann]

Closing in favor of https://github.com/sveltejs/kit/issues/8033. Please see the recommended solution there