Buffer allocation and encoding in Node.js - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Buffer allocation code?

Consider the following Node.js code snippet. What will be logged to the console?

Node.js

const buf = Buffer.alloc(5, 'a');
console.log(buf.toString());

A "aaaaa"

B "aaaa"

C "\u0000\u0000\u0000\u0000\u0000"

D "a\u0000\u0000\u0000\u0000"

💡 Hint

Buffer.alloc(size, fill) fills the buffer with the given value.

Buffer.alloc(5, 'a') creates a buffer of length 5 filled with the byte for 'a'. Converting to string shows 'aaaaa'.

❓ Predict Output

intermediate

What does this Buffer.from() call output?

What will be the output of this code snippet?

Node.js

const buf = Buffer.from('hello', 'utf8');
console.log(buf.length);

A 6

B 4

C 5

D 10

💡 Hint

Each ASCII character is 1 byte in UTF-8.

The string 'hello' has 5 characters, each encoded as 1 byte in UTF-8, so buffer length is 5.

❓ Predict Output

advanced

What error does this Buffer allocation code raise?

What error will this code produce when run in Node.js?

Node.js

const buf = Buffer.alloc(-1);

A TypeError: Buffer size must be a number

B RangeError: The value of "size" is out of range. It must be >= 0 and <= 2147483647. Received -1

C SyntaxError: Unexpected token '-'

D No error, creates empty buffer

💡 Hint

Buffer size must be a non-negative integer.

Buffer.alloc() throws a RangeError if the size is negative.

❓ Predict Output

advanced

What is the output of this Buffer encoding conversion?

What will this code print to the console?

Node.js

const buf = Buffer.from('café', 'utf8');
console.log(buf.toString('latin1'));

A "caf?"

B "café"

C "cafÃ"

D "café"

💡 Hint

UTF-8 bytes interpreted as Latin1 characters can produce unexpected characters.

The UTF-8 bytes for 'é' are two bytes, which when read as Latin1 produce 'é'.

❓ component_behavior

expert

How many bytes does this Buffer contain after slicing?

Given this code, what is the length of the resulting buffer?

Node.js

const buf = Buffer.from('hello world', 'utf8');
const slice = buf.slice(6, 11);
console.log(slice.length);

A 5

B 6

C 11

D 10

💡 Hint

Buffer.slice(start, end) includes bytes from start up to but not including end.

Slice from index 6 to 11 includes 5 bytes: 'world'.