Reading and writing buffer data in Node.js - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a Buffer from a string.

Node.js

const buf = Buffer.[1]('Hello');

Drag options to blanks, or click blank then click option'

Awrite

Bfrom

Calloc

Dslice

Attempts:

3 left

💡 Hint

Common Mistakes

Using Buffer.alloc() which creates an empty buffer of a fixed size.

Trying to use Buffer.write() which writes data into an existing buffer.

The Buffer.from() method creates a new buffer containing the given string.

2fill in blank

medium

Complete the code to write the string 'Hi' into the buffer at offset 0.

Node.js

buf.[1]('Hi', 0);

Drag options to blanks, or click blank then click option'

Awrite

Bfill

Ccopy

Dslice

Attempts:

3 left

💡 Hint

Common Mistakes

Using fill() which fills the buffer with a value but not a string.

Using copy() which copies data between buffers.

The write() method writes a string to the buffer starting at the specified offset.

3fill in blank

hard

Fix the error in reading an unsigned 16-bit integer from the buffer at offset 2.

Node.js

const num = buf.[1](2);

Drag options to blanks, or click blank then click option'

AreadUInt16BE

BreadInt16LE

CreadUInt8

DreadInt32BE

Attempts:

3 left

💡 Hint

Common Mistakes

Using readUInt8 which reads only 1 byte.

Using readInt32BE which reads 4 bytes instead of 2.

readUInt16BE reads an unsigned 16-bit integer in big-endian format from the buffer at the given offset.

4fill in blank

hard

Fill both blanks to create a buffer of length 5 and fill it with the byte value 0x1F.

Node.js

const buf = Buffer.[1](5);
buf.[2](0x1F);

Drag options to blanks, or click blank then click option'

Aalloc

Bfrom

Cfill

Dwrite

Attempts:

3 left

💡 Hint

Common Mistakes

Using Buffer.from() which creates a buffer from data, not size.

Using write() which writes string data, not fills the buffer.

Buffer.alloc(5) creates a buffer of length 5, and fill(0x1F) fills it with the byte value 0x1F.

5fill in blank

hard

Fill all three blanks to create a buffer from a string, write 'OK' at offset 3, and read an unsigned 8-bit integer at offset 4.

Node.js

const buf = Buffer.[1]('Example');
buf.[2]('OK', 3);
const val = buf.[3](4);

Drag options to blanks, or click blank then click option'

Afrom

Bwrite

CreadUInt8

Dalloc

Attempts:

3 left

💡 Hint

Common Mistakes

Using Buffer.alloc() instead of Buffer.from() to create buffer from string.

Using readInt8 instead of readUInt8 for unsigned reading.

Buffer.from('Example') creates a buffer from the string. write('OK', 3) writes 'OK' starting at offset 3. readUInt8(4) reads one byte as an unsigned integer at offset 4.

Practice

1. What is the primary purpose of a Buffer in Node.js?

easy

A. To manage HTTP requests automatically

B. To store JavaScript objects in memory

C. To hold raw binary data for reading and writing

D. To format strings for display in the console

Solution

1. Step 1: Understand what Buffer stores

   A Buffer is designed to hold raw binary data, not objects or formatted strings.

2. Step 2: Identify Buffer's main use

   Buffers allow reading and writing bytes directly, useful for binary data handling.

3. Final Answer:

   To hold raw binary data for reading and writing -> Option C

4. Quick Check:

   Buffer = raw binary data [OK]

Hint: Buffers store raw bytes, not objects or formatted text [OK]

Common Mistakes:

• Thinking Buffer stores JavaScript objects
• Confusing Buffer with string formatting tools
• Assuming Buffer manages HTTP requests

2. Which of the following is the correct way to create a Buffer of size 5 bytes filled with zeros?

easy

A. Buffer.new(5)

B. Buffer.alloc(5)

C. new Buffer(5, 0)

D. Buffer.create(5)

Solution

1. Step 1: Recall Buffer creation methods

   In modern Node.js, Buffer.alloc(size) creates a zero-filled buffer.

2. Step 2: Check other options

   Buffer.new and Buffer.create do not exist; new Buffer() is deprecated and unsafe.

3. Final Answer:

   Buffer.alloc(5) -> Option B

4. Quick Check:

   Use Buffer.alloc for safe zero-filled buffers [OK]

Hint: Use Buffer.alloc(size) for zero-filled buffers [OK]

Common Mistakes:

• Using deprecated new Buffer() constructor
• Trying non-existent Buffer.new or Buffer.create methods
• Not initializing buffer contents

3. What will be the output of this code?

const buf = Buffer.from('abc');
console.log(buf[1]);

medium

A. 98

B. b

C. 1

D. undefined

Solution

1. Step 1: Understand Buffer.from and indexing

   Buffer.from('abc') creates a buffer with ASCII codes of 'a', 'b', 'c'. Index 1 is 'b'.

2. Step 2: Check what buf[1] returns

   Buffer indexes return the byte value (number), not the character. 'b' ASCII code is 98.

3. Final Answer:

   98 -> Option A

4. Quick Check:

   Buffer index returns byte code, not character [OK]

Hint: Buffer indexes return byte numbers, not characters [OK]

Common Mistakes:

• Expecting character instead of ASCII code
• Confusing index with string position
• Assuming buf[1] returns a string

4. Identify the error in this code snippet:

const buf = Buffer.alloc(3);
buf.write('hello');
console.log(buf.toString());

medium

A. Buffer size is too small for the string 'hello'

B. Buffer.alloc cannot be used with write method

C. toString() cannot be called on a Buffer

D. write method requires encoding argument

Solution

1. Step 1: Check buffer size vs string length

   Buffer.alloc(3) creates 3 bytes, but 'hello' needs 5 bytes to store fully.

2. Step 2: Understand write behavior

   write writes as many bytes as fit; here it truncates 'hello' to 'hel'.

3. Final Answer:

   Buffer size is too small for the string 'hello' -> Option A

4. Quick Check:

   Buffer too small truncates written string [OK]

Hint: Buffer must be large enough to hold full string [OK]

Common Mistakes:

• Thinking write needs encoding argument always
• Assuming toString() is invalid on Buffer
• Believing Buffer.alloc disallows write

5. You want to copy the first 4 bytes from one buffer src to another buffer dest starting at index 2 in dest. Which code correctly does this?

hard

A. dest.copy(src, 2, 0, 4);

B. dest.copy(src, 0, 2, 6);

C. src.copy(dest, 0, 2, 6);

D. src.copy(dest, 2, 0, 4);

Solution

1. Step 1: Understand Buffer.copy parameters

   The method is source.copy(target, targetStart, sourceStart, sourceEnd).

2. Step 2: Match parameters to requirement

   Copy from src starting at 0 to 4 bytes, into dest starting at index 2.

3. Final Answer:

   src.copy(dest, 2, 0, 4); -> Option D

4. Quick Check:

   source.copy(target, targetStart, sourceStart, sourceEnd) [OK]

Hint: source.copy(target, targetStart, sourceStart, sourceEnd) [OK]

Common Mistakes:

• Swapping source and target buffers
• Mixing up start and end indexes
• Using copy on wrong buffer object