有没有base64转化的相关代码？

import util from '@ohos.util'; 
 
let base64 = new util.Base64Helper(); 
 
let str = 'LTI0LC04MiwtOTUsLTI1LC04MiwtMTA1L' 
 
let arr = base64.decodeSync(str);//base64格式转 uint8Array 
 
let baseStr = base64.encodeToStringSync(arr);// uint8Array转base64