Environment variables on Deploy in Deno - Mini Project: Build & Apply

Environment variables on Deploy with Deno

📖 Scenario: You are building a small Deno application that needs to use environment variables to store sensitive information like API keys. This is important because you don't want to hardcode secrets in your code when deploying your app.

🎯 Goal: Learn how to set up environment variables in Deno and access them safely in your code for deployment.

📋 What You'll Learn

Create an environment variable file with a key-value pair

Load environment variables using Deno's standard library

Access the environment variable in your code

Use the environment variable in a simple function

💡 Why This Matters

🌍 Real World

Many applications need to keep secrets like API keys safe and not hardcoded. Using environment variables is a standard way to do this, especially when deploying apps.

💼 Career

Understanding environment variables and how to use them in Deno is essential for backend developers and anyone deploying secure applications.

1

Create a .env file with an API key

Create a file named .env with the exact content API_KEY=12345secret to store your API key.

Deno

# Create a .env file with API_KEY=12345secret
# Your code here

Hint

Use a plain text file named .env and write API_KEY=12345secret inside it.

2

Load environment variables using Deno dotenv

In your main.ts file, import config from "https://deno.land/std/dotenv/mod.ts" and create a constant called env by calling await config().

Deno

import { config } from "https://deno.land/std/dotenv/mod.ts"

// Load environment variables
# Your code here

Hint

Use await config() to load variables from the .env file into env.

3

Access the API key from the loaded environment variables

Use the constant env to create a variable called apiKey that stores the value of the environment variable API_KEY.

Deno

import { config } from "https://deno.land/std/dotenv/mod.ts"

const env = await config()

// Get API key from env
# Your code here

Hint

Access the API key with env.API_KEY and assign it to apiKey.

4

Use the API key in a function to simulate deployment usage

Write a function called showApiKey that returns a string `Your API key is: ${apiKey}`. Then export this function as the default export.

Deno

import { config } from "https://deno.land/std/dotenv/mod.ts"

const env = await config()

const apiKey = env.API_KEY

// Create and export showApiKey function
# Your code here

Hint

Define showApiKey to return the string with the API key and export it as default.

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