HarmonyOS 字符串的base64加解密工具类未找到

可以参考如下代码：

let textEncoder = new util.TextEncoder("utf-8");
let input='{"act":"GetPurchased","uid":"10074013","page":1,"tag":1,"flg":1,"title":"刘"}';
let shuzu= textEncoder.encodeInto(input)
hilog.info(0xFF00, "testTag",'解密前'+JSON.stringify(shuzu));
let that = new util.Base64Helper();
let result = that.encodeToStringSync(shuzu);
let waitDecodeArr = that.decodeSync(result)
let textDecoder = util.TextDecoder.create('utf-8')
let decodeResult = textDecoder.decodeWithStream(waitDecodeArr)
hilog.info(0xFF00, "testTag",'解压后'+decodeResult);

参考链接：

https://developer.huawei.com/consumer/cn/doc/harmonyos-references-V5/js-apis-util-V5#textdecoder