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process.stdin/stdout

Learn streams with process.stdin/stdout.

process.stdin and stdout

process.stdin and process.stdout are the standard input and output streams. stdin reads data from the keyboard or a pipe; stdout writes output to the screen. console.log is actually a wrapper around stdout.

process.stdout.write("hello") prints the output but, unlike console.log, it does not add a newline at the end. This is useful when you want to write several pieces on the same line. stdin is a Readable stream; you can read incoming data with process.stdin.on("data", cb). This lets you build interactive CLI tools.

write versus console.log

The main difference between process.stdout.write and console.log is the newline. console.log automatically adds \n after each call; write does not.

For example, process.stdout.write("A"); process.stdout.write("B"); gives the output AB, side by side on one line. Doing the same with console.log would show A and B on separate lines. For progress bars, percentage indicators or updating the same line, write is preferred. Because it works as a stream, write is also more efficient for large outputs.

Practice Write two pieces to stdout

Write two pieces side by side with process.stdout.write("Node") and process.stdout.write("JS"). Do not add a newline.

Starter code

index.js
// Write "Node" to stdout
// Write "JS" to stdout
// write here

Sample solution

index.js
process.stdout.write("Node");
process.stdout.write("JS");

Expected output

NodeJS

Questions and answers

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

1 What kind of object is process.stdin?

index.js
process.stdin
  • A string
  • Readable stream Correct answer
  • A number
  • An array

Explanation: stdin is a Readable stream; you read data in chunks.

2 Write to stdout

Question 
process.____.write("Node");
Answer 
process.stdout.write("Node");

Explanation: stdout.write prints without a newline.

3 Match each piece to its role

Term Meaning
stdin Input stream
stdout Output stream
write Writes without newline
console.log Writes with newline

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