Buffer.from(arrayBuffer[, byteOffset[, length]])

• arrayBuffer <ArrayBuffer> | <SharedArrayBuffer> ArrayBuffer、SharedArrayBuffer，例如 TypedArray 的 .buffer 属性。
• byteOffset <integer> 要暴露的第一个字节的索引。 默认值: 0。
• length <integer> 要暴露的字节数。 默认值: arrayBuffer.byteLength - byteOffset。

这将创建 ArrayBuffer 的视图，而无需复制底层内存。 例如，当传入对 TypedArray 实例的 .buffer 属性的引用时，新创建的 Buffer 将与 TypedArray 的底层 ArrayBuffer 共享相同的分配内存。

import { Buffer } from 'node:buffer';

const arr = new Uint16Array(2);

arr[0] = 5000;
arr[1] = 4000;

// 与 `arr` 共享内存。
const buf = Buffer.from(arr.buffer);

console.log(buf);
// 打印: <Buffer 88 13 a0 0f>

// 更改原始的 Uint16Array 也会更改缓冲区。
arr[1] = 6000;

console.log(buf);
// 打印: <Buffer 88 13 70 17>const { Buffer } = require('node:buffer');

const arr = new Uint16Array(2);

arr[0] = 5000;
arr[1] = 4000;

// 与 `arr` 共享内存。
const buf = Buffer.from(arr.buffer);

console.log(buf);
// 打印: <Buffer 88 13 a0 0f>

// 更改原始的 Uint16Array 也会更改缓冲区。
arr[1] = 6000;

console.log(buf);
// 打印: <Buffer 88 13 70 17>

可选的 byteOffset 和 length 参数指定了 arrayBuffer 中将由 Buffer 共享的内存范围。

import { Buffer } from 'node:buffer';

const ab = new ArrayBuffer(10);
const buf = Buffer.from(ab, 0, 2);

console.log(buf.length);
// 打印: 2const { Buffer } = require('node:buffer');

const ab = new ArrayBuffer(10);
const buf = Buffer.from(ab, 0, 2);

console.log(buf.length);
// 打印: 2

如果 arrayBuffer 不是 ArrayBuffer 或 SharedArrayBuffer 或其他适用于 Buffer.from() 变体的类型，则将抛出 TypeError。

记住，支持 ArrayBuffer 可以覆盖超出 TypedArray 视图边界的内存范围。 使用 TypedArray 的 buffer 属性创建的新 Buffer 可能会超出 TypedArray 的范围：

import { Buffer } from 'node:buffer';

const arrA = Uint8Array.from([0x63, 0x64, 0x65, 0x66]); // 4 个元素
const arrB = new Uint8Array(arrA.buffer, 1, 2); // 2 个元素
console.log(arrA.buffer === arrB.buffer); // true

const buf = Buffer.from(arrB.buffer);
console.log(buf);
// 打印: <Buffer 63 64 65 66>const { Buffer } = require('node:buffer');

const arrA = Uint8Array.from([0x63, 0x64, 0x65, 0x66]); // 4 个元素
const arrB = new Uint8Array(arrA.buffer, 1, 2); // 2 个元素
console.log(arrA.buffer === arrB.buffer); // true

const buf = Buffer.from(arrB.buffer);
console.log(buf);
// 打印: <Buffer 63 64 65 66>

• arrayBuffer <ArrayBuffer> | <SharedArrayBuffer> An ArrayBuffer, SharedArrayBuffer, for example the .buffer property of a TypedArray.
• byteOffset <integer> Index of first byte to expose. Default: 0.
• length <integer> Number of bytes to expose. Default: arrayBuffer.byteLength - byteOffset.

This creates a view of the ArrayBuffer without copying the underlying memory. For example, when passed a reference to the .buffer property of a TypedArray instance, the newly created Buffer will share the same allocated memory as the TypedArray's underlying ArrayBuffer.

import { Buffer } from 'node:buffer';

const arr = new Uint16Array(2);

arr[0] = 5000;
arr[1] = 4000;

// Shares memory with `arr`.
const buf = Buffer.from(arr.buffer);

console.log(buf);
// Prints: <Buffer 88 13 a0 0f>

// Changing the original Uint16Array changes the Buffer also.
arr[1] = 6000;

console.log(buf);
// Prints: <Buffer 88 13 70 17>const { Buffer } = require('node:buffer');

const arr = new Uint16Array(2);

arr[0] = 5000;
arr[1] = 4000;

// Shares memory with `arr`.
const buf = Buffer.from(arr.buffer);

console.log(buf);
// Prints: <Buffer 88 13 a0 0f>

// Changing the original Uint16Array changes the Buffer also.
arr[1] = 6000;

console.log(buf);
// Prints: <Buffer 88 13 70 17>

The optional byteOffset and length arguments specify a memory range within the arrayBuffer that will be shared by the Buffer.

import { Buffer } from 'node:buffer';

const ab = new ArrayBuffer(10);
const buf = Buffer.from(ab, 0, 2);

console.log(buf.length);
// Prints: 2const { Buffer } = require('node:buffer');

const ab = new ArrayBuffer(10);
const buf = Buffer.from(ab, 0, 2);

console.log(buf.length);
// Prints: 2

A TypeError will be thrown if arrayBuffer is not an ArrayBuffer or a SharedArrayBuffer or another type appropriate for Buffer.from() variants.

It is important to remember that a backing ArrayBuffer can cover a range of memory that extends beyond the bounds of a TypedArray view. A new Buffer created using the buffer property of a TypedArray may extend beyond the range of the TypedArray:

import { Buffer } from 'node:buffer';

const arrA = Uint8Array.from([0x63, 0x64, 0x65, 0x66]); // 4 elements
const arrB = new Uint8Array(arrA.buffer, 1, 2); // 2 elements
console.log(arrA.buffer === arrB.buffer); // true

const buf = Buffer.from(arrB.buffer);
console.log(buf);
// Prints: <Buffer 63 64 65 66>const { Buffer } = require('node:buffer');

const arrA = Uint8Array.from([0x63, 0x64, 0x65, 0x66]); // 4 elements
const arrB = new Uint8Array(arrA.buffer, 1, 2); // 2 elements
console.log(arrA.buffer === arrB.buffer); // true

const buf = Buffer.from(arrB.buffer);
console.log(buf);
// Prints: <Buffer 63 64 65 66>