如何实现字符串编解码

import { util } from '@kit.ArkTS'; 
// ... 
// 创建编码器 
let textEncoder = new util.TextEncoder('gbk'); 
let buffer = new ArrayBuffer(20); 
let result = new Uint8Array(buffer); 
// 编码 
result = textEncoder.encodeInto('hello'); 
this.arr = new Uint8Array(result.length) 
for (let i = 0; i < result.length; i++) { 
  this.arr[i] = result[i]; 
} 
// 创建解码器 
let textDecoder = util.TextDecoder.create('gbk') 
// 解码 
let retStr = textDecoder.decodeWithStream(this.arr);