Buffer to string conversion in Node.js - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Node.js Buffer to string conversion?

Consider the following code snippet that converts a buffer to a string. What will be printed to the console?

Node.js

const buf = Buffer.from([72, 101, 108, 108, 111]);
console.log(buf.toString());

A "undefined"

B "[72,101,108,108,111]"

C "Buffer(5)"

D "Hello"

💡 Hint

Think about what the buffer contains and what toString() does by default.

The buffer contains ASCII codes for the letters H, e, l, l, o. Calling toString() converts these codes to their character equivalents, resulting in the string "Hello".

❓ Predict Output

intermediate

What does this code output when specifying encoding?

What will this code print to the console?

Node.js

const buf = Buffer.from('68656c6c6f', 'hex');
console.log(buf.toString('utf8'));

A "hello"

B "68656c6c6f"

C "undefined"

D "\u6865\u6c6c\u6f"

💡 Hint

The buffer is created from hex values representing ASCII characters.

The buffer is created from the hex string representing the ASCII codes for "hello". Converting it to a UTF-8 string prints "hello".

❓ component_behavior

advanced

What happens if you convert a buffer with invalid UTF-8 bytes to string?

Given this buffer with invalid UTF-8 bytes, what will be the output of toString()?

Node.js

const buf = Buffer.from([0xff, 0xfe, 0xfd]);
console.log(buf.toString('utf8'));

A "\xff\xfe\xfd"

B Throws a SyntaxError

C "���"

D "" (empty string)

💡 Hint

Invalid UTF-8 bytes are replaced with a special character when converted to string.

Invalid UTF-8 bytes are replaced by the Unicode replacement character � (U+FFFD) when converted to string, so the output is three replacement characters.

📝 Syntax

advanced

Which option correctly converts a buffer to a base64 string?

Select the code snippet that correctly converts a buffer to a base64 encoded string.

A const b64 = buf.toString('base64');

B const b64 = buf.encode('base64');

C const b64 = Buffer.toString(buf, 'base64');

D const b64 = buf.toBase64();

💡 Hint

Check the Buffer API for the correct method and parameter to convert to base64.

The toString method accepts an encoding parameter like 'base64' to convert the buffer to a base64 string. Other methods do not exist or are incorrect.

🔧 Debug

expert

Why does this buffer to string conversion produce unexpected output?

This code is intended to convert a buffer to a UTF-8 string, but the output is garbled. What is the most likely cause?

Node.js

const buf = Buffer.from('c3a9', 'utf8');
console.log(buf.toString());

A Buffer.from() cannot accept strings, only arrays

B The input string is hex but encoded as UTF-8, causing wrong bytes in buffer

C toString() requires an encoding parameter to decode properly

D The buffer is empty, so output is empty string

💡 Hint

Consider what the input string represents and how Buffer.from interprets it with the given encoding.

The string 'c3a9' is a hex representation but is passed as a UTF-8 string, so the buffer contains bytes for characters 'c', '3', 'a', '9' instead of the intended hex bytes. This causes garbled output.