buf[index]

• index <integer>

索引运算符 [index] 可用于获取和设置 buf 中位置 index 处的八位字节。 这些值是指单个字节，因此合法值范围介于 0x00 和 0xFF（十六进制）或 0 和 255（十进制）之间。

该运算符继承自 Uint8Array，因此其越界访问行为与 Uint8Array 相同。 换句话说，当 index 为负或大于等于 buf.length 时，buf[index] 返回 undefined，如果 index 为负或 >= buf.length，buf[index] = value 不修改缓冲区。

// 每次一个字节地将 ASCII 字符串复制到 `Buffer` 中。
// （这仅适用于 ASCII-only 字符串。通常，应该使用 `Buffer.from()` 来执行此转换。）

const str = 'Node.js';
const buf = Buffer.allocUnsafe(str.length);

for (let i = 0; i < str.length; i++) {
  buf[i] = str.charCodeAt(i);
}

console.log(buf.toString('utf8'));
// 打印: Node.js

• index <integer>

The index operator [index] can be used to get and set the octet at position index in buf. The values refer to individual bytes, so the legal value range is between 0x00 and 0xFF (hex) or 0 and 255 (decimal).

This operator is inherited from Uint8Array, so its behavior on out-of-bounds access is the same as Uint8Array. In other words, buf[index] returns undefined when index is negative or greater or equal to buf.length, and buf[index] = value does not modify the buffer if index is negative or >= buf.length.

// Copy an ASCII string into a `Buffer` one byte at a time.
// (This only works for ASCII-only strings. In general, one should use
// `Buffer.from()` to perform this conversion.)

const str = 'Node.js';
const buf = Buffer.allocUnsafe(str.length);

for (let i = 0; i < str.length; i++) {
  buf[i] = str.charCodeAt(i);
}

console.log(buf.toString('utf8'));
// Prints: Node.js