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process.env

Learn environment variables with process.env.

What is process.env?

process.env is an object that holds environment variables. It gives Node.js access to the variables defined by the operating system. It is used for configuration data like port numbers, database addresses and API keys.

For example, if you start with PORT=3000 node app.js, then process.env.PORT is "3000". A variable that is not defined returns undefined, so the pattern process.env.PORT || 3000 is common to give a default. This way the same code can run with different settings in development and production.

Setting environment variables

You can set environment variables in two ways. On the command line you can pass them before starting: PORT=3000 node app.js. Or you can set them from code with process.env.PORT = "3000".

The first way is safer, because secret keys are not written into the code. The second way is fine for tests and temporary settings. In production, .env files and the dotenv package are also used; but these are not built in, they are installed with npm install. The key point is to keep configuration separate from code, so the code runs unchanged in different environments.

Practice Read the port and print it

Read the port variable with process.env.PORT. If it is not defined, use 3000 as a default with ||. Print it with console.log.

Starter code

index.js
// Read the port from the environment
// If missing, use 3000
// Print with console.log
// write here

Sample solution

index.js
const port = process.env.PORT || 3000;
console.log(port);

Expected output

3000

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 Read the port variable

Question 
const port = process.env.____ || 3000;
Answer 
const port = process.env.PORT || 3000;

Explanation: PORT is read from the environment.

2 What does process.env.PORT return if not defined?

index.js
process.env.PORT
  • It throws an error
  • An empty string
  • 3000
  • undefined Correct answer

Explanation: An undefined variable returns undefined; that is why || gives a default.

3 Match each piece to its role

Term Meaning
process.env Environment variables
PORT A variable name
|| Default value
undefined Undefined result

All lessons in Intermediate

1 Events

  1. EventEmitter
  2. on and emit
  3. once
  4. removeListener
  5. error event
  6. Summary - Events

2 Streams

  1. What are streams?
  2. Readable stream
  3. Writable stream
  4. pipe
  5. Transform stream
  6. Summary - Streams

3 HTTP server

  1. http.createServer
  2. Request and response
  3. Routing
  4. JSON response
  5. Query string
  6. Summary - HTTP server

4 Project: Helper library

  1. Module design
  2. String helpers
  3. Number helpers
  4. Date helpers
  5. Putting it together

5 Express basics

  1. What is Express?
  2. express()
  3. app.get
  4. app.post
  5. app.listen
  6. Summary - Express basics

6 Middleware

  1. What is middleware?
  2. app.use
  3. Router middleware
  4. Error middleware
  5. Body parser
  6. Summary - Middleware

7 Routing

  1. Route parameters
  2. Query parameters
  3. express.Router
  4. Route groups
  5. Method chaining
  6. Summary - Routing

8 Project: Quiz app

  1. Quiz model
  2. Adding questions
  3. Running the quiz
  4. Score calculation
  5. Putting it together

9 Async patterns

  1. Async iteration
  2. Async generators
  3. Concurrency limit
  4. Retry pattern
  5. Debounce and throttle
  6. Summary - Async patterns

10 Buffer and binary

  1. What is Buffer?
  2. Buffer.from
  3. Buffer.concat
  4. toString and encoding
  5. Buffer slice
  6. Summary - Buffer

11 Process and CLI

  1. process.argv
  2. process.env
  3. process.exit
  4. process.stdin/stdout
  5. Child process
  6. Summary - Process

12 Project: Library API

  1. Model design
  2. Express app
  3. CRUD routes
  4. Middleware
  5. Putting it together

13 npm and packages

  1. npm install
  2. package.json scripts
  3. devDependencies
  4. Semver
  5. npm publish
  6. Summary - npm

14 Error handling

  1. The Error class
  2. try/catch
  3. Custom errors
  4. Error middleware
  5. Unhandled rejection
  6. Summary - Error handling

15 Testing basics

  1. node:test
  2. assert
  3. describe and it
  4. Before and after
  5. Mock
  6. Summary - Testing basics

16 Debugging

  1. node inspect
  2. Chrome DevTools
  3. console methods
  4. util.inspect
  5. Source maps
  6. Summary - Debugging

17 Date and time

  1. The Date object
  2. Date methods
  3. Intl.DateTimeFormat
  4. performance.now
  5. setTimeout and setInterval
  6. Summary - Date and time

18 Crypto

  1. crypto module
  2. createHash
  3. randomBytes
  4. HMAC
  5. AES
  6. Summary - Crypto

19 URL and query string

  1. URL object
  2. URLSearchParams
  3. URL properties
  4. URL.resolve
  5. querystring
  6. Summary - URL and query string

20 Intermediate final

  1. Project design
  2. Express API
  3. fs persistence
  4. Middleware
  5. Putting it together