So SvelteKit is super awesome n' all and the best thing ever but have
you ever tried to use a .env secret that you didn't want exposed on
the client?

SvelteKit uses Vite and it has a specific way to reference Env
Variables and Modes, you reference a .env variable with
import.meta.env.VITE_NAME_OF_VARIABLE the VITE_* prefix means in
SvelteKit it makes that variable available on the client.

What if you have a secret key?

So if you want a secret key that's not exposed to the client then,
what? Remove the VITE_* prefix? Well, no, so, how to have secrets??

The answer is don't use Vite and instead use something to load the
variables from the .env file.

Use env-cmd or dotenv or whatever you want to use to ensure the
runtime process.env is populated in dev.

Example

Here I have defined my .env file at the root of my project:

VITE_CLIENT_VARIABLE=wheeeeeeeee
SUPER_SECRET_SECRET=shhhhhh

Then I've created a secret.js file to access my secret:

export const API_URL = process.env['SUPER_SECRET_SECRET']

Then I've added env-cmd to my dev script in my package.json so
that process.env has the super secret secret populated:

"scripts": {
  "dev": "env-cmd svelte-kit dev",

Now I can access my super secret secret and have client side variables
too.

Update

There's annother option to use which I found on the Blog by
Hideckies in their example it's a svelte.config.js change:

const config = {
  kit: {
    // ...
    vite: {
      define: {
        'process.env': process.env,
      },
    },
  },
}

export default config

Check out the post linked earlier for more info!

Thanks!

A kind thank you to Discord users Xyo and especially saikatdas0790
on the Svelte Discord svelte-kit channel for helping me out with
this!