Buffer類：

Buffer物件是Node處理二進位制資料的一個介面。它是Node原生提供的全域性物件，可以直接使用，不需要require(‘buffer’)。Buffer本質上就是位元組陣列

構造方法（類）：例項化buf物件

Buffer.from(array)：

let buf = Buffer.from([0x62, 0x75, 0x66, 0x66, 0x65, 0x72]);
console.log(buf.toString());

Buffer.from(string)：

let buf = Buffer.from('hello','utf8');
console.log(buf);
 

Buffer.alloc(size)：

let buf = Buffer.alloc(5);
console.log(buf);

靜態方法：

Buffer.isEncoding() 判斷是否支援該編碼

console.log(Buffer.isEncoding('utf8'));
console.log(Buffer.isEncoding('gbk'));

Buffer.isBuffer() 判斷是否為Buffer

let buf = Buffer.from('hello');
console.log(Buffer.isBuffer(buf));
console.log(Buffer.isBuffer({}));
 

Buffer.byteLength() 返回指定編碼的位元組長度，預設utf8

let buf = Buffer.from('中國','utf8');
console.log(Buffer.byteLength(buf));
console.log(buf.toString());
let buf1 = Buffer.from('中國','ascii');
console.log(Buffer.byteLength(buf1));
console.log(buf1.toString());

Buffer.concat() 將一組Buffer物件合併為一個Buffer物件

3);
let buf2 = Buffer.alloc(5);
let buf3 = Buffer.concat([buf1,buf2]);
console.log(Buffer.byteLength(buf3));
 

let buf1 = Buffer.from('tom');
let buf2 = Buffer.from('jerry');
let buf3 = Buffer.concat([buf1,buf2]);
console.log(Buffer.byteLength(buf3));
console.log(buf3.toString());

例項方法：

write() 向buffer物件中寫入內容

let buf = Buffer.alloc(5);
console.log(buf);

let buf = Buffer.alloc(5);
buf.write('hello');
console.log(buf);

let buf = Buffer.alloc(5);
buf.write('hello',2);
console.log(buf);

let buf = Buffer.alloc(5);
buf.write('hello',2,2);
console.log(buf);

slice() 擷取新的buffer物件

toString() 把buf物件轉成字串

let buf = Buffer.from('hello');
let buf1 = buf.slice(1,4);
console.log(buf === buf1);//false
console.log(buf1.toString());

toJson() 把buf物件轉成json形式的字串

// toJSON方法不需要顯式（強制轉換）呼叫，當JSON.stringify方法呼叫的時候會自動呼叫toJSON方法
// const buf = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5]);
const buf = Buffer.from('hello');
const json = JSON.stringify(buf);
console.log(json);