Buffer.from(object[, offsetOrEncoding[, length]])

• object <Object> 支持 Symbol.toPrimitive 或 valueOf() 的对象。
• offsetOrEncoding <integer> | <string> 字节偏移量或编码。
• length <integer> 长度。

对于 valueOf() 函数返回的值不严格等于 object 的对象，则返回 Buffer.from(object.valueOf(), offsetOrEncoding, length)。

const buf = Buffer.from(new String('this is a test'));
// 打印: <Buffer 74 68 69 73 20 69 73 20 61 20 74 65 73 74>

对于支持 Symbol.toPrimitive 的对象，则返回 Buffer.from(object[Symbol.toPrimitive]('string'), offsetOrEncoding)。

class Foo {
  [Symbol.toPrimitive]() {
    return 'this is a test';
  }
}

const buf = Buffer.from(new Foo(), 'utf8');
// 打印: <Buffer 74 68 69 73 20 69 73 20 61 20 74 65 73 74>

如果 object 没有提到的方法或不是适合 Buffer.from() 变体的另一种类型，则将抛出 TypeError。

• object <Object> An object supporting Symbol.toPrimitive or valueOf().
• offsetOrEncoding <integer> | <string> A byte-offset or encoding.
• length <integer> A length.

For objects whose valueOf() function returns a value not strictly equal to object, returns Buffer.from(object.valueOf(), offsetOrEncoding, length).

const buf = Buffer.from(new String('this is a test'));
// Prints: <Buffer 74 68 69 73 20 69 73 20 61 20 74 65 73 74>

For objects that support Symbol.toPrimitive, returns Buffer.from(object[Symbol.toPrimitive]('string'), offsetOrEncoding).

class Foo {
  [Symbol.toPrimitive]() {
    return 'this is a test';
  }
}

const buf = Buffer.from(new Foo(), 'utf8');
// Prints: <Buffer 74 68 69 73 20 69 73 20 61 20 74 65 73 74>

A TypeError will be thrown if object does not have the mentioned methods or is not of another type appropriate for Buffer.from() variants.