Streams vs loading entire file in memory in Node.js - Practice Questions

Challenge - 5 Problems

🧠 Conceptual

intermediate

Why use streams instead of loading entire files?

Which of the following best explains why streams are preferred over loading an entire file into memory in Node.js?

A Streams allow processing data piece by piece, reducing memory usage for large files.

B Streams automatically compress files to save disk space.

C Loading entire files is faster and uses less CPU than streams.

D Streams require the entire file to be loaded before processing starts.

💡 Hint

Think about memory use when files are very large.

Streams process data in chunks, so they don't need to load the whole file at once. This saves memory especially for big files.

❓ component_behavior

intermediate

What happens when reading a large file with streams?

Given this Node.js code snippet using streams, what will be the output behavior?

Node.js

const fs = require('fs');
const stream = fs.createReadStream('largefile.txt');
stream.on('data', chunk => {
  console.log('Received chunk of size:', chunk.length);
});
stream.on('end', () => {
  console.log('Finished reading file');
});

A Reads the entire file at once and logs one chunk size.

B Logs 'Finished reading file' immediately, then logs chunk sizes.

C Throws an error because 'data' event is not supported on streams.

D Logs multiple 'Received chunk of size:' messages as data arrives, then logs 'Finished reading file'.

💡 Hint

Streams emit 'data' events multiple times as chunks arrive.

The 'data' event fires repeatedly for each chunk. After all chunks are read, the 'end' event fires.

📝 Syntax

advanced

Identify the error in this stream reading code

What error will this Node.js code produce when trying to read a file using streams?

Node.js

const fs = require('fs');
const stream = fs.createReadStream('file.txt');
stream.on('data', (chunk) => {
  console.log(chunk.toString());
});
stream.on('finish', () => {
  console.log('Done reading');
});

A No error; logs file content and 'Done reading'.

B SyntaxError due to missing semicolon.

C Error: 'finish' event does not exist on readable streams.

D TypeError because chunk is undefined.

💡 Hint

Check if 'finish' is the right event for reading streams.

The 'finish' event is for writable streams. Readable streams emit 'end' when done.

❓ state_output

advanced

Memory usage difference between streams and full file read

If you read a 1GB file using fs.readFile versus fs.createReadStream, what is the expected memory usage behavior?

A Both use the same memory because Node.js caches files automatically.

B fs.readFile uses much more memory because it loads the entire file; streams use less memory by processing chunks.

C Streams use more memory because they keep multiple chunks in memory at once.

D fs.readFile uses less memory because it reads faster.

💡 Hint

Think about how much data is held in memory at once.

fs.readFile loads the whole file into memory, which can be large. Streams handle small parts at a time, saving memory.

🔧 Debug

expert

Why does this stream pipeline hang without output?

Consider this Node.js code that reads a file and writes to another file using streams. Why does it hang without finishing?

Node.js

const fs = require('fs');
const readStream = fs.createReadStream('input.txt');
const writeStream = fs.createWriteStream('output.txt');
readStream.pipe(writeStream);
// No event handlers attached

A The code is correct; it should finish but no logs show because no events are handled.

B The writeStream is not closed, so the process waits indefinitely.

C The readStream is not paused, causing a deadlock.

D The pipe method is missing a callback to start the flow.

💡 Hint

Think about what happens if no logs or events are used.

The pipe works and copies data, but without event handlers, you won't see output or know when it finishes. The process ends when streams close.