#     
## What is `copy()` in `Node.js`?

The **`copy()` method** of the `Buffer` class in `Node.js` copies data from a `Buffer` object to another `Buffer` object. 

The data is copied regardless of whether the memory regions of the `Buffer` objects overlap.

The process is illustrated below.

#     
## Syntax

The prototype of the `copy()` method is shown below.

---
```Node.js
buf.copy(target, targetStart, sourceStart, sourceEnd);
```
---

> The keyword `buf` represents any `Buffer` object in `Node.js`.

## Parameters

The `copy()` method accepts the following parameters:

* `target`: The `Buffer` object into which the data is to be copied.

* `targetStart`: The offset of the destination `Buffer` from which to start writing data. By default, this parameter has a value of $0$.

* `sourceStart`: The offset of source buffer `buf` from which to start copying data. By default, this parameter has a value of $0$.

* `sourceEnd`: The offset of source buffer `buf` from which to stop copying data. By default, this parameter is equal to the length of `buf`.

## Return value

The `copy()` method returns an integer that represents the number of copied bytes.

#   
## Code

The code below shows how the `copy()` method can be used in `Node.js`.

// initialize buffer objects
var bufferOne = Buffer.from('World');
var bufferTwo = Buffer.from('Hello');

var bufferThree = Buffer.from('Buffers');
var bufferFour = Buffer.from('Learning Node.js with Educative');

// copy bufferOne to bufferTwo
console.log("Before calling copy(), bufferTwo is: ", bufferTwo.toString())
var bytes = bufferOne.copy(bufferTwo)

console.log("After calling copy(), bufferTwo is: ", bufferTwo.toString())
console.log("Copied", bytes, "bytes.\n");

// copy subset of bufferThree to bufferFour
console.log("Before calling copy(), bufferFour is: ", bufferFour.toString())
bytes = bufferThree.copy(bufferFour, 9);

console.log("After calling copy(), bufferFour is: ", bufferFour.toString())
console.log("Copied", bytes, "bytes");

#     
## Explanation

- First, we initialize multiple `Buffer` objects through the `from()` method. Each `Buffer` has a unique value.

- The `copy()` method in line $10$ copies all of `bufferOne` into `bufferTwo`. Since no values are provided for the `targetStart`, `sourceStart`, and `sourceEnd` parameters, the `copy()` method takes their default values as $0$, $0$, and $5$, respectively.

- Similarly, the `copy()` method in line $15$ copies all of `bufferThree` into `bufferFour`, starting at the specified offset, i.e., index $9$ of `bufferFour`. 

- Since `bufferThree` contains $6$ characters, indices $9-15$ are overwritten in `bufferFour`. Originally, these indices contained the characters `Node.js`, but after the `copy()` method is invoked, the characters from `bufferThree` are copied into these indices.

---
> For more details about the `Buffer` class in `Node.js`, please check the [documentation](https://nodejs.org/api/buffer.html).

What is the Buffer.copy() method in Node.js?

Copies data between Buffer objects irrespective of overlapping, returning copied byte count.

What is the Buffer.copy() method in Node.js?

What is copy() in Node.js?

Syntax

Parameters

Return value

Code

Explanation

What is `copy()` in `Node.js`?