Environment variables on Deploy in Deno

Introduction

Environment variables let you keep secret or changeable info outside your code. This helps keep your app safe and flexible when you deploy it.

You want to keep API keys secret and not put them in your code.

You need to change settings like database URLs without changing your code.

You want to use different values for development and production easily.

You want to avoid hardcoding passwords or tokens in your app.

You want to configure your app behavior depending on where it runs.

Syntax

Deno

const value = Deno.env.get("VARIABLE_NAME");

Use Deno.env.get to read environment variables in Deno.

Environment variables are strings or null if not set.

Examples

Reads the API_KEY environment variable and prints it.

Deno

const apiKey = Deno.env.get("API_KEY");
console.log(apiKey);

Reads PORT or uses default 8000 if not set.

Deno

const port = Deno.env.get("PORT") || "8000";
console.log(`Server runs on port ${port}`);

Checks if DATABASE_URL is set and warns if missing.

Deno

if (!Deno.env.get("DATABASE_URL")) {
  console.error("Missing DATABASE_URL environment variable!");
}

Sample Program

This simple Deno server reads the PORT environment variable to decide which port to listen on. If PORT is not set, it uses 8080 by default. It then starts a server that responds with a greeting message.

Deno

import { serve } from "https://deno.land/std@0.201.0/http/server.ts";

const port = Deno.env.get("PORT") || "8080";

console.log(`Server running on http://localhost:${port}/`);

serve((_req) => new Response("Hello from Deno!"), { port: +port });

Important Notes

Remember to set environment variables in your deployment platform settings or shell before running your Deno app.

Use deno run --allow-env to allow your program to access environment variables.

Never commit sensitive environment variables to public code repositories.

Summary

Environment variables keep secrets and settings outside your code.

Use Deno.env.get("NAME") to read them in Deno.

Set variables in your deployment environment to change app behavior safely.

Practice

1. What is the main purpose of environment variables when deploying a Deno application?

easy

A. To keep secrets and settings outside the code for security and flexibility

B. To write all configuration directly inside the source code

C. To make the application run faster by hardcoding values

D. To store user data permanently on the server

Solution

1. Step 1: Understand environment variables role

   Environment variables store secrets and settings outside the code to avoid exposing sensitive data.

2. Step 2: Recognize deployment best practices

   Keeping secrets outside code allows changing settings without modifying the app, improving security and flexibility.

3. Final Answer:

   To keep secrets and settings outside the code for security and flexibility -> Option A

4. Quick Check:

   Environment variables = external secrets/settings [OK]

Hint: Environment variables hold secrets outside code [OK]

Common Mistakes:

• Thinking environment variables are for storing user data
• Hardcoding secrets inside source code
• Believing environment variables speed up code execution

2. Which of the following is the correct way to read an environment variable named API_KEY in a Deno script?

easy

A. const key = getenv("API_KEY");

B. const key = process.env.API_KEY;

C. const key = Deno.env.get("API_KEY");

D. const key = env.API_KEY;

Solution

1. Step 1: Recall Deno environment variable syntax

   Deno uses Deno.env.get("NAME") to access environment variables.

2. Step 2: Compare options

   const key = Deno.env.get("API_KEY"); matches Deno syntax; others are from Node.js or incorrect.

3. Final Answer:

   const key = Deno.env.get("API_KEY"); -> Option C

4. Quick Check:

   Deno.env.get("API_KEY") = correct syntax [OK]

Hint: Use Deno.env.get("VAR_NAME") to read env variables [OK]

Common Mistakes:

• Using Node.js syntax like process.env in Deno
• Calling undefined functions like getenv
• Accessing env variables without Deno.env.get

3. Given the following Deno code snippet deployed with environment variable PORT=8080, what will be the output?

const port = Deno.env.get("PORT") || "3000";
console.log(`Server running on port ${port}`);

medium

A. Server running on port 3000

B. Server running on port 8080

C. Server running on port undefined

D. Error: PORT is not defined

Solution

1. Step 1: Check environment variable value

   The environment variable PORT is set to "8080" in deployment.

2. Step 2: Evaluate fallback logic

   The code uses Deno.env.get("PORT") || "3000", so it uses "8080" because PORT exists.

3. Final Answer:

   Server running on port 8080 -> Option B

4. Quick Check:

   PORT=8080 overrides default 3000 [OK]

Hint: Env var set? Use it; else fallback value [OK]

Common Mistakes:

• Assuming fallback value always prints
• Expecting error if env var exists
• Confusing undefined with fallback

4. You deployed a Deno app but reading environment variables returns undefined. Which fix will solve this problem?

medium

A. Restart the app without setting variables

B. Change Deno.env.get to process.env

C. Hardcode variables inside the source code

D. Set environment variables in the deployment platform settings

Solution

1. Step 1: Identify cause of undefined env variables

   Undefined means variables are not set in the deployment environment.

2. Step 2: Apply correct fix

   Setting environment variables in deployment platform ensures Deno.env.get can read them.

3. Final Answer:

   Set environment variables in the deployment platform settings -> Option D

4. Quick Check:

   Env vars must be set in deploy settings [OK]

Hint: Always set env vars in deployment platform [OK]

Common Mistakes:

• Using Node.js syntax in Deno
• Hardcoding secrets instead of setting env vars
• Restarting app without setting variables

5. You want to deploy a Deno app that uses an environment variable MODE to switch between 'development' and 'production'. Which approach correctly uses environment variables to change app behavior safely?

hard

A. Set MODE in deployment settings and use Deno.env.get("MODE") in code to conditionally run features

B. Hardcode const MODE = "production" in source code and redeploy to change

C. Use a config file checked into source with MODE value

D. Ask users to input MODE at runtime every time

Solution

1. Step 1: Understand environment variable usage for modes

   Environment variables allow switching modes without changing code.

2. Step 2: Choose safe and flexible method

   Setting MODE in deployment and reading it with Deno.env.get enables safe conditional logic.

3. Final Answer:

   Set MODE in deployment settings and use Deno.env.get("MODE") in code to conditionally run features -> Option A

4. Quick Check:

   Env vars control modes safely without code changes [OK]

Hint: Use env vars to toggle modes, not hardcoding [OK]

Common Mistakes:

• Hardcoding mode and redeploying for changes
• Storing secrets or modes in config files checked into source
• Asking users to input mode every run