Buffer concatenation in Node.js - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Buffer concatenation code?

Consider the following Node.js code that concatenates two buffers. What will be the output when logged as a string?

Node.js

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

A "Hello, World!"

B "Hello World!"

C "Hello,World!"

D "HelloWorld!"

💡 Hint

Remember that Buffer.concat joins buffers exactly as they are without adding extra characters.

Buffer.concat joins the buffers in the order given, preserving all characters including spaces and punctuation. Since buf1 ends with a comma and space, the output includes them exactly.

❓ Predict Output

intermediate

What is the length of the concatenated Buffer?

Given these buffers, what is the length of the resulting buffer after concatenation?

Node.js

const buf1 = Buffer.from('abc');
const buf2 = Buffer.from('defg');
const result = Buffer.concat([buf1, buf2]);
console.log(result.length);

A 4

B 6

C 8

D 7

💡 Hint

Length counts all bytes in both buffers combined.

Buffer 'abc' has length 3, 'defg' has length 4, so concatenated length is 3 + 4 = 7.

🔧 Debug

advanced

Why does this Buffer.concat call throw an error?

Examine the code below. Why does it throw a TypeError?

Node.js

const buf1 = Buffer.from('test');
const buf2 = 'not a buffer';
const result = Buffer.concat([buf1, buf2]);

A Because buf2 is a string, not a Buffer instance

B Because buf1 is not initialized correctly

C Because Buffer.concat requires at least three buffers

D Because Buffer.concat only accepts a single buffer argument

💡 Hint

Buffer.concat expects an array of Buffer objects only.

Buffer.concat throws a TypeError if any element in the array is not a Buffer instance. Here, buf2 is a string, causing the error.

❓ component_behavior

advanced

What happens if you specify a total length smaller than the sum of buffers in Buffer.concat?

Consider this code snippet. What will be the output of the concatenated buffer as a string?

Node.js

const buf1 = Buffer.from('12345');
const buf2 = Buffer.from('67890');
const result = Buffer.concat([buf1, buf2], 8);
console.log(result.toString());

A "1234567"

B "12345678"

C "1234567890"

D "123456789"

💡 Hint

The total length limits the size of the resulting buffer.

Buffer.concat with a total length of 8 returns a buffer of length 8 containing the first 8 bytes from the concatenated buffers, which is "12345678".

📝 Syntax

expert

Which option correctly concatenates buffers and converts to uppercase string?

Choose the code snippet that concatenates two buffers and outputs the uppercase string of the result.

A

const buf1 = Buffer.from('foo');
const buf2 = Buffer.from('bar');
const result = Buffer.concat([buf1, buf2]).toUpperCase();
console.log(result.toString());

B

const buf1 = Buffer.from('foo');
const buf2 = Buffer.from('bar');
const result = Buffer.concat(buf1, buf2);
console.log(result.toString().toUpperCase());

C

const buf1 = Buffer.from('foo');
const buf2 = Buffer.from('bar');
const result = Buffer.concat([buf1, buf2]);
console.log(result.toString().toUpperCase());

D

const buf1 = Buffer.from('foo');
const buf2 = Buffer.from('bar');
const result = Buffer.concat([buf1, buf2]);
console.log(result.toUpperCase());

💡 Hint

Remember Buffer.concat takes an array of buffers and toUpperCase() is a string method.

Option C correctly concatenates buffers, converts to string, then to uppercase. Option C passes arguments incorrectly. Option C calls toUpperCase on a Buffer, causing error. Option C calls toUpperCase on Buffer, causing error.