Creating buffers in Node.js - Practice Exercises

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Node.js buffer code?

Consider the following code snippet that creates a buffer and writes a string into it. What will be logged to the console?

Node.js

const buf = Buffer.alloc(5);
buf.write('HelloWorld');
console.log(buf.toString());

A Hello

B Error: Buffer overflow

C Hello\u0000

D HelloWorld

💡 Hint

Buffer.alloc creates a fixed size buffer. Writing beyond its size truncates the string.

Buffer.alloc(5) creates a buffer of length 5. Writing 'HelloWorld' writes only the first 5 characters 'Hello'. The rest is ignored. So buf.toString() outputs 'Hello'.

❓ Predict Output

intermediate

What does this Buffer.from() call produce?

What will be the output of this code snippet?

Node.js

const buf = Buffer.from([65, 66, 67, 68]);
console.log(buf.toString());

A ABCD

B [65,66,67,68]

C 65666768

D Error: Invalid argument

💡 Hint

Buffer.from with an array creates a buffer with those byte values.

The array [65,66,67,68] corresponds to ASCII codes for 'A', 'B', 'C', 'D'. Buffer.from creates a buffer with those bytes. toString() converts bytes to string 'ABCD'.

❓ Predict Output

advanced

What error does this buffer code raise?

What error will this code produce when run?

Node.js

const buf = Buffer.allocUnsafe(3);
buf.write('NodeJS', 0, 10);
console.log(buf.toString());

A SyntaxError: Unexpected token

B TypeError: Invalid argument

C No error, outputs 'NodeJS'

D RangeError: Attempt to write outside buffer bounds

💡 Hint

Writing more bytes than buffer size causes a range error.

Buffer.allocUnsafe(3) creates a buffer of length 3. Trying to write 10 bytes starting at 0 exceeds buffer size, causing a RangeError.

❓ component_behavior

advanced

How does Buffer.concat behave with empty buffers?

Given the following code, what will be the output?

Node.js

const buf1 = Buffer.from('Hello');
const buf2 = Buffer.alloc(0);
const buf3 = Buffer.from('World');
const result = Buffer.concat([buf1, buf2, buf3]);
console.log(result.toString());

A Hello\u0000World

B HelloWorld

C Hello

D World

💡 Hint

Buffer.concat ignores empty buffers and joins the rest.

Buffer.concat joins all buffers in order. Empty buffers add no content. So the result is 'Hello' + '' + 'World' = 'HelloWorld'.

📝 Syntax

expert

Which option correctly creates a zero-filled buffer of length 4?

Select the code snippet that creates a buffer of length 4 filled with zeros without any warnings or errors.

A const buf = new Buffer(4);

B const buf = Buffer.from(4);

C const buf = Buffer.alloc(4);

D const buf = Buffer.allocUnsafe(4).fill(0);

💡 Hint

Buffer.alloc creates zero-filled buffers safely.

Buffer.alloc(4) creates a zero-filled buffer of length 4 safely. Buffer.from(4) is invalid. Buffer.allocUnsafe(4) creates uninitialized buffer, but fill(0) fills it with zeros (valid but less preferred). new Buffer(4) is deprecated and unsafe.