process.stdin and process.stdout in Node.js - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What will this Node.js code output when you type 'hello' and press Enter?

Consider this code snippet that reads from standard input and writes to standard output:

Node.js

process.stdin.on('data', (data) => {
  process.stdout.write(`You typed: ${data}`);
});
process.stdin.resume();

A

You typed: hello

B olleh :depyt uoY

C hello

D Error: Cannot read data

💡 Hint

Remember that the data event includes the newline character when you press Enter.

The 'data' event receives a Buffer or string including the newline character from pressing Enter. The code writes it back with 'You typed: ' prefix, so the output includes the newline.

📝 Syntax

intermediate

Which option correctly sets up process.stdin to read input as UTF-8 strings?

You want to read user input as strings, not buffers. Which code snippet does this correctly?

A process.stdin.encoding('utf8');

B process.stdin.encoding = 'utf8';

C process.stdin.setEncoding = 'utf8';

D process.stdin.setEncoding('utf8');

💡 Hint

Look for the method that sets encoding properly.

The correct method to set encoding is setEncoding('utf8'). Other options are invalid syntax or properties.

🔧 Debug

advanced

Why does this code never print anything after input?

Look at this code snippet:

Node.js

process.stdin.on('data', (chunk) => {
  console.log(chunk.toString());
});

// No other code

A Because chunk is empty string always

B Because console.log is asynchronous and buffers output

C Because process.stdin is paused by default and never resumed

D Because 'data' event never fires on process.stdin

💡 Hint

Check if the stream is flowing or paused by default.

In Node.js, process.stdin is paused by default. Without calling process.stdin.resume(), the 'data' event won't fire.

❓ state_output

advanced

What is the output of this code after typing 'abc' and pressing Enter?

This code reads input and writes it back in uppercase:

Node.js

process.stdin.setEncoding('utf8');
process.stdin.on('data', (data) => {
  process.stdout.write(data.toUpperCase());
});
process.stdin.resume();

A

ABC

B cba

C BC

D abc

💡 Hint

Remember the input includes the newline character.

The input 'abc' plus newline is converted to uppercase, so output is 'ABC\n'.

🧠 Conceptual

expert

What happens if you write to process.stdout without a newline and then read from process.stdin?

Consider this code snippet:

Node.js

process.stdout.write('Enter your name: ');
process.stdin.setEncoding('utf8');
process.stdin.on('data', (data) => {
  process.stdout.write(`Hello, ${data}`);
  process.exit();
});
process.stdin.resume();

A The prompt appears with a newline, waits for input, then greets without newline

B The prompt appears without a newline, waits for input, then greets with input including newline

C The prompt does not appear until after input is entered

D The program crashes because process.exit() is called inside the data event

💡 Hint

process.stdout.write does not add a newline automatically.

process.stdout.write prints exactly what you give it, so the prompt appears without newline. Then input is read and greeted including the newline from input.