Environment variables ($env) in Svelte - Cheat Sheet & Quick Revision

Recall & Review

beginner

What are environment variables in Svelte?

Environment variables are special values set outside your code that your app can use to store settings like API keys or mode (development or production). They help keep sensitive info safe and make your app flexible.

intermediate

How do you access environment variables in SvelteKit using $env?

You import <code>$env/static/private</code> or <code>$env/static/public</code> to access variables at build time, or <code>$env/dynamic/private</code> and <code>$env/dynamic/public</code> for runtime access. Public variables start with <code>PUBLIC_</code> and are safe to expose to the browser.

beginner

Why should environment variables starting with PUBLIC_ be used carefully?

Variables starting with PUBLIC_ are exposed to the browser, so they should not contain secrets like passwords or private keys. Use them only for safe, public info like API URLs.

intermediate

What is the difference between static and dynamic environment variables in SvelteKit?

Static variables are replaced at build time and cannot change after. Dynamic variables are read at runtime, allowing changes without rebuilding the app.

beginner

How do you add environment variables to your SvelteKit project?

Create a .env file in your project root and add variables like API_KEY=12345. Then restart the dev server to load them. Use PUBLIC_ prefix for variables you want available in the browser.

Which prefix should you use for environment variables that need to be accessible in the browser in SvelteKit?

A PRIVATE_

B PUBLIC_

C SECRET_

D CLIENT_

Only variables starting with PUBLIC_ are exposed to the browser in SvelteKit.

Where do you import static environment variables from in SvelteKit?

A process.env

B $env/dynamic/private or $env/dynamic/public

C import.meta.env

D $env/static/private or $env/static/public

Static environment variables are imported from $env/static/private or $env/static/public in SvelteKit.

What happens if you change a static environment variable after building your SvelteKit app?

A The variable is ignored

B The app updates automatically

C The app must be rebuilt to see the change

D The app crashes

Static variables are baked into the build, so you must rebuild the app to apply changes.

Which file do you typically use to define environment variables in a SvelteKit project?

A .env

B config.js

C package.json

D index.html

Environment variables are usually defined in a .env file at the project root.

Why should secret keys NOT be prefixed with PUBLIC_ in SvelteKit?

A Because PUBLIC_ variables are exposed to the browser

B Because PUBLIC_ variables are ignored

C Because PUBLIC_ variables are encrypted

D Because PUBLIC_ variables are only for server use

PUBLIC_ variables are sent to the browser, so secrets should never use this prefix.

Explain how to use environment variables in a SvelteKit app, including how to keep secrets safe.

Think about build time vs runtime and public vs private variables.

Describe the difference between static and dynamic environment variables in SvelteKit and when to use each.

Consider when your app needs to read the variable.

Practice

1. What is the main reason to use environment variables in a Svelte project?

easy

A. To avoid using any external libraries

B. To write all code inside a single file

C. To make the app run faster by skipping variables

D. To store settings outside the code for safety and flexibility

Solution

1. Step 1: Understand environment variables purpose

   Environment variables keep sensitive or changeable settings outside the main code, so you can change them without editing code.

2. Step 2: Connect to safety and flexibility

   This separation helps keep secrets safe and lets you adjust settings easily for different environments like development or production.

3. Final Answer:

   To store settings outside the code for safety and flexibility -> Option D

4. Quick Check:

   Environment variables = safety and flexibility [OK]

Hint: Environment variables keep secrets outside code [OK]

Common Mistakes:

• Thinking environment variables speed up the app
• Believing environment variables are for code organization only
• Confusing environment variables with libraries

2. Which import statement correctly accesses public environment variables in a Svelte component?

easy

A. import { PUBLIC_API_KEY } from '$env/static/public';

B. import { API_KEY } from '$env/static/private';

C. import { API_KEY } from '$env/dynamic/private';

D. import { PUBLIC_API_KEY } from '$env/dynamic/public';

Solution

1. Step 1: Identify public environment variable import

   Public variables are accessed from '$env/static/public' when known at build time.

2. Step 2: Match variable prefix and import path

   Public variables must start with 'PUBLIC_' and be imported from '$env/static/public' for static access.

3. Final Answer:

   import { PUBLIC_API_KEY } from '$env/static/public'; -> Option A

4. Quick Check:

   Public vars use static/public import [OK]

Hint: Public vars use $env/static/public import [OK]

Common Mistakes:

• Using private import paths for public variables
• Forgetting the PUBLIC_ prefix
• Mixing dynamic and static imports incorrectly

3. Given this Svelte code snippet, what will be displayed if the environment variable PUBLIC_APP_NAME is set to 'MyApp'?

import { PUBLIC_APP_NAME } from '$env/static/public';

<h1>Welcome to {PUBLIC_APP_NAME}!</h1>

medium

A. Welcome to MyApp!

B. Welcome to PUBLIC_APP_NAME!

C. Welcome to !

D. Error: Cannot find variable PUBLIC_APP_NAME

Solution

1. Step 1: Understand import of PUBLIC_APP_NAME

   The variable PUBLIC_APP_NAME is imported from '$env/static/public', so its value is available at build time.

2. Step 2: Check usage in template

   The variable is used inside the <h1> tag, so it will display the actual value 'MyApp'.

3. Final Answer:

   <h1>Welcome to MyApp!</h1> -> Option A

4. Quick Check:

   Static public env var shows actual value [OK]

Hint: Static public vars show real value in template [OK]

Common Mistakes:

• Expecting variable name instead of value
• Assuming variable is undefined without import
• Confusing static and dynamic imports

4. You try to access a private environment variable in a Svelte component using this code:

import { SECRET_KEY } from '$env/static/private';

console.log(SECRET_KEY);

But you get an error during build. What is the likely cause?

medium

A. SECRET_KEY must start with PUBLIC_ prefix

B. You must import from '$env/dynamic/public' instead

C. Private variables cannot be imported in client-side code

D. You forgot to declare SECRET_KEY in .env file

Solution

1. Step 1: Understand private env variable usage

   Private environment variables are only available on the server side and cannot be imported into client-side code.

2. Step 2: Recognize build error cause

   Importing private variables in a component that runs in the browser causes build errors because secrets must stay server-only.

3. Final Answer:

   Private variables cannot be imported in client-side code -> Option C

4. Quick Check:

   Private vars are server-only [OK]

Hint: Private vars only on server, not client [OK]

Common Mistakes:

• Adding PUBLIC_ prefix to private vars
• Using dynamic public import for private vars
• Assuming missing .env declaration causes build error

5. You want to show a greeting message in your Svelte app that changes based on a public environment variable PUBLIC_GREETING. You also want to update this message without rebuilding the app. Which approach should you use?

hard

A. Import PUBLIC_GREETING from $env/static/public and use it directly

B. Import PUBLIC_GREETING from $env/dynamic/public and use it in your component

C. Store PUBLIC_GREETING in a local variable inside the component

D. Hardcode the greeting message in the component

Solution

1. Step 1: Understand static vs dynamic public env variables

   Static public variables are fixed at build time, so changes require rebuilding the app.

2. Step 2: Use dynamic public env for runtime updates

   Dynamic public variables from '$env/dynamic/public' reflect environment changes without rebuilding, ideal for updating messages.

3. Final Answer:

   Import PUBLIC_GREETING from $env/dynamic/public and use it in your component -> Option B

4. Quick Check:

   Dynamic public env allows runtime updates [OK]

Hint: Use $env/dynamic/public for runtime env changes [OK]

Common Mistakes:

• Using static public import for dynamic needs
• Storing env vars in local variables without import
• Hardcoding messages instead of using env vars