buf.copy(target[, targetStart[, sourceStart[, sourceEnd]]])

• target <Buffer> | <Uint8Array> 一个 Buffer 或 <Uint8Array>，用于复制数据的目标。
• targetStart <integer> 在 target 中开始写入的偏移量。默认值： 0。
• sourceStart <integer> 在 buf 中开始复制的偏移量。默认值： 0。
• sourceEnd <integer> 在 buf 中停止复制的偏移量（不包括该位置）。默认值： buf.length。
• 返回值：<integer> 被复制的字节数。

将数据从 buf 的一个区域复制到 target 的一个区域，即使 target 内存区域与 buf 重叠也可以。

【Copies data from a region of buf to a region in target, even if the target memory region overlaps with buf.】

TypedArray.prototype.set() 执行相同的操作，适用于所有 TypedArray，包括 Node.js 的 Buffer，尽管它所需的函数参数不同。

import { Buffer } from 'node:buffer';

// Create two `Buffer` instances.
const buf1 = Buffer.allocUnsafe(26);
const buf2 = Buffer.allocUnsafe(26).fill('!');

for (let i = 0; i < 26; i++) {
  // 97 is the decimal ASCII value for 'a'.
  buf1[i] = i + 97;
}

// Copy `buf1` bytes 16 through 19 into `buf2` starting at byte 8 of `buf2`.
buf1.copy(buf2, 8, 16, 20);
// This is equivalent to:
// buf2.set(buf1.subarray(16, 20), 8);

console.log(buf2.toString('ascii', 0, 25));
// Prints: !!!!!!!!qrst!!!!!!!!!!!!!const { Buffer } = require('node:buffer');

// Create two `Buffer` instances.
const buf1 = Buffer.allocUnsafe(26);
const buf2 = Buffer.allocUnsafe(26).fill('!');

for (let i = 0; i < 26; i++) {
  // 97 is the decimal ASCII value for 'a'.
  buf1[i] = i + 97;
}

// Copy `buf1` bytes 16 through 19 into `buf2` starting at byte 8 of `buf2`.
buf1.copy(buf2, 8, 16, 20);
// This is equivalent to:
// buf2.set(buf1.subarray(16, 20), 8);

console.log(buf2.toString('ascii', 0, 25));
// Prints: !!!!!!!!qrst!!!!!!!!!!!!!拷贝

import { Buffer } from 'node:buffer';

// Create a `Buffer` and copy data from one region to an overlapping region
// within the same `Buffer`.

const buf = Buffer.allocUnsafe(26);

for (let i = 0; i < 26; i++) {
  // 97 is the decimal ASCII value for 'a'.
  buf[i] = i + 97;
}

buf.copy(buf, 0, 4, 10);

console.log(buf.toString());
// Prints: efghijghijklmnopqrstuvwxyzconst { Buffer } = require('node:buffer');

// Create a `Buffer` and copy data from one region to an overlapping region
// within the same `Buffer`.

const buf = Buffer.allocUnsafe(26);

for (let i = 0; i < 26; i++) {
  // 97 is the decimal ASCII value for 'a'.
  buf[i] = i + 97;
}

buf.copy(buf, 0, 4, 10);

console.log(buf.toString());
// Prints: efghijghijklmnopqrstuvwxyz拷贝