What is Buffer?

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.

Exercise Create a buffer and print it

Create a four-byte buffer with Buffer.alloc(4). Print it with console.log.

Show example solution

const buf = Buffer.alloc(4);
console.log(buf);

Test yourself

What is Buffer used for?
```
Buffer.alloc(4)
```
- To work with binary data
- Only to store text
- To define classes
- To manipulate the DOM
Show answer

To work with binary data — Buffer holds binary data at the byte level.

Create a buffer

const buf = Buffer.____(4);

Show answer

const buf = Buffer.alloc(4);

Match each piece to its role

Buffer

Holds binary data
buf.length

Gives byte count
buf[0]

Accesses first byte
0-255

Value range of a byte

Next lesson: Buffer.from

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