process is not defined

Process needs to be replaced using a plugin:

For example:

```
import { sveltekit } from '@sveltejs/kit/vite';
import { defineConfig } from 'vite';
import replace from '@rollup/plugin-replace';

const mode = process.env.NODE_ENV;

export default defineConfig({
	plugins: [sveltekit(), replace({
		'process.browser': true,
		'process.env.NODE_ENV': JSON.stringify(mode)
	}),]
});
```