Environment & Config

Configuration is the set of values that change between machines — ports, database URLs, API keys — which you keep out of your code and read from environment variables on process.env .

Learn Environment & Config in our free Node.js course — a beginner-friendly interactive lesson with worked examples, a practice exercise and a quick reference.

Part of the free Node.js course at LearnCodingFast — hands-on lessons with examples you run in your browser, plus practice exercises and a quick quiz.

By the end of this lesson you'll read environment variables with sensible defaults, load a .env file natively, convert string values to the right types, and centralize everything in a validated config module.

What You'll Learn in This Lesson

1️⃣ Reading process.env

Node puts every environment variable on the process.env object. Read a value, supply a default with ?? for when it's missing, and remember that every value is a string — convert with Number() when you need a number.

2️⃣ Loading a .env File

Typing variables on every launch gets old. A .env file holds KEY=value lines, and recent Node loads it natively with --env-file . Keep that file out of git so secrets stay private.

3️⃣ A Central, Validated Config Module

Reading process.env scattered across files gets messy. The clean pattern: a single config.js that reads, validates, and exports one object. Required values throw at startup if missing, so the app fails fast instead of breaking mysteriously later.

Your turn. Fill in the two ___ blanks to read a host and port with defaults, then run it.

Build a real config.js with a required() helper, a number, a required string, and a boolean parsed from a string. Import it in app.js and print all three values.

📋 Quick Reference — Config in Node

Practice quiz

Where does Node expose environment variables?

  • process.argv
  • global.config
  • process.env
  • os.env

Answer: process.env. process.env is an object of environment variables provided by the OS or launch command.

What type is every value in process.env?

  • A string
  • A number
  • A boolean
  • It varies by key

Answer: A string. Environment variables come from the OS as text, so every process.env value is a string.

What does process.env.PORT ?? 3000 do?

  • Always uses 3000
  • Multiplies PORT by 3000
  • Throws if PORT is set
  • Uses 3000 only when PORT is undefined

Answer: Uses 3000 only when PORT is undefined. The ?? operator supplies the default 3000 only when process.env.PORT is null or undefined.

How do you turn process.env.WORKERS into a real number?

  • parseEnv(process.env.WORKERS)
  • Number(process.env.WORKERS)
  • process.env.WORKERS.toNumber()
  • It is already a number

Answer: Number(process.env.WORKERS). Use Number(...) to convert the string env value into a numeric type.

How can modern Node (v20.6+) load a .env file natively?

  • node --env-file=.env app.js
  • node --load-env app.js
  • require('dotenv') is required
  • node --config .env

Answer: node --env-file=.env app.js. Node v20.6+ reads a .env file with the --env-file flag, populating process.env before your code runs.

How do you set a variable inline for one launch?

  • node app.js PORT=8080
  • node --PORT 8080 app.js
  • PORT=8080 node app.js
  • export only in package.json

Answer: PORT=8080 node app.js. Prefixing the command, like PORT=8080 node app.js, sets the variable for that run.

What is the recommended way to handle config across your app?

  • Read process.env everywhere it is needed
  • Read env vars once in a config module and export a clean object
  • Hard-code values in each file
  • Store config in a global variable

Answer: Read env vars once in a config module and export a clean object. Best practice: read and validate env vars in one config module; the rest of the app imports config, not process.env.

How should a required env var behave when it is missing?

  • Silently default to an empty string
  • Retry until it appears
  • Log a warning and continue
  • Fail fast and loud by throwing an error at startup

Answer: Fail fast and loud by throwing an error at startup. Validate required values at startup and throw, so the app fails loudly instead of misbehaving later.

How do you convert a string env var to a boolean?

  • Boolean(process.env.DEBUG)
  • Compare it: process.env.DEBUG === 'true'
  • process.env.DEBUG.toBool()
  • It is already a boolean

Answer: Compare it: process.env.DEBUG === 'true'. Because env values are strings, the string 'false' is truthy; compare explicitly with === 'true'.

How do you keep secrets like API keys out of version control?

  • Commit them in the README
  • Encrypt the whole repo
  • Add .env to .gitignore and commit a .env.example instead
  • Put them in package.json

Answer: Add .env to .gitignore and commit a .env.example instead. Add .env to .gitignore so secrets are never pushed; commit a .env.example listing variable names with placeholders.