What is Buffer?
- Node.js course
- Intermediate
- Lesson 53/116
- 5 min
Learn binary data management with Buffer.
What is Buffer?
A Buffer in Node.js is an object that holds fixed-size binary data. It allocates raw memory outside the V8 heap. You use it whenever you work with byte sequences: file reading, network streams and cryptography.
Regular JavaScript arrays can hold numbers, but each element carries overhead. A Buffer works directly at the byte level: every element is a value from 0 to 255. You create one with Buffer.alloc(4), which fills four bytes with zeros. The output shows <Buffer 00 00 00 00>.
The structure of a Buffer
A buffer's length is fixed when it is created and cannot change. The buf.length property gives the byte count. You can access each byte with buf[i], which returns a number from 0 to 255.
For example Buffer.from("Ab") makes a two-byte buffer: buf[0] is 65 (the ASCII code of A) and buf[1] is 98. Buffers are mutable: writing buf[0] = 66 turns the first byte into the letter B. Unlike strings, a buffer's contents can be changed in place.
Practice Create a buffer and print it
Create a four-byte buffer with Buffer.alloc(4). Print it with console.log.
Starter code
// Create a four-byte buffer
// write here
// Print the buffer
// write hereSample solution
const buf = Buffer.alloc(4);
console.log(buf);Expected output
<Buffer 00 00 00 00>
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What is Buffer used for?
Buffer.alloc(4)- To work with binary data Correct answer
- Only to store text
- To define classes
- To manipulate the DOM
Explanation: Buffer holds binary data at the byte level.
2 Create a buffer
const buf = Buffer.____(4);const buf = Buffer.alloc(4);Explanation: Buffer.alloc(4) creates a four-byte zero-filled buffer.
3 Match each piece to its role
| Term | Meaning |
|---|---|
Buffer |
Holds binary data |
buf.length |
Gives byte count |
buf[0] |
Accesses first byte |
0-255 |
Value range of a byte |