baidu了一堆，发现基本都需要下载并调用第三方组件，嫌麻烦，最后找到这篇文章：https://www.cnblogs.com/index-html/p/js-str-to-gbk-ultra-lite.html
在他的基础上完善了该方法，调用方式： 
decStr2 = GBKencodeURIComponent(decStr1);
decStr3 = GBKdecodeURIComponent(decStr2);

简单纯粹

<input type="button" value="GBK编解码测试" onclick="textDecodeZxy();" /><br>
原始值：<input type="text" id="iddecStr1" style="width:80%"/><br>
编码值：<input type="text" id="iddecStr2" style="width:80%"/><br>
解码值：<input type="text" id="iddecStr3" style="width:80%">
<script language='javascript'>
//GBK(GB2312)解码对照表
const tableEn = new Uint16Array(65536);
//GBK(GB2312)编码对照表
const tableEn2 = new Uint16Array(65536);
//Unicode字符|GBK(GB2312)和UTF-8对应关系
const rangesEn = [[0xA1, 0xA9, 0xA1, 0xFE],[0xB0, 0xF7, 0xA1, 0xFE],[0x81, 0xA0, 0x40, 0xFE],[0xAA, 0xFE, 0x40, 0xA0],[0xA8, 0xA9, 0x40, 0xA0],[0xAA, 0xAF, 0xA1, 0xFE],[0xF8, 0xFE, 0xA1, 0xFE],[0xA1, 0xA7, 0x40, 0xA0],
];
//UTF-8对照表
const codesEn = new Uint16Array(23940);
//编码初始化
function initEnCode() {let i = 0;for (const[b1Begin, b1End, b2Begin, b2End]of rangesEn) {for (let b2 = b2Begin; b2 <= b2End; b2++) {if (b2 !== 0x7F) {for (let b1 = b1Begin; b1 <= b1End; b1++) {codesEn[i++] = b2 << 8 | b1;}}}}const str = new TextDecoder('gbk').decode(codesEn);for (let i = 0; i < str.length; i++) {tableEn[str.charCodeAt(i)] = codesEn[i];tableEn2[codesEn[i]] = str.charCodeAt(i);}
}initEnCode();
/*初始全局变量*///GBK(GB2312)字节转字符串
function gbkToStr(buf){var strResult = "";var strIndex = 0;for(let i = 0; i < buf.length; i++) {if(buf[i] < 0x80){strResult += String.fromCharCode(buf[i]);strIndex ++;}else if(buf[i] >= 0x80 && buf[i + 1] >= 0x80){var codeIndex =  buf[i+1] << 8 | buf[i];var code = tableEn2[codeIndex]strResult += String.fromCharCode(code);i ++;strIndex += 2;}}return strResult;
}//字符串转GBK(GB2312)
function stringToGbk(str) {initEnCode();const buf = new Uint8Array(str.length * 2);let n = 0;for (let i = 0; i < str.length; i++) {const code = str.charCodeAt(i);if (code < 0x80) {buf[n++] = code;} else {const gbk = tableEn[code];buf[n++] = gbk & 0xFF;buf[n++] = gbk >> 8;}}return buf.subarray(0, n);
}//GBK(GB2312)编码
function GBKencodeURIComponent(objTag){var strResult = "";var bytary = stringToGbk(objTag);for(var i = 0; i < bytary.length; i ++){if(bytary[i] < 0x80){strResult += encodeURIComponent(String.fromCharCode(bytary[i]));}else{strResult += "%"+bytary[i].toString(16).toUpperCase();}}return strResult;
}//GBK(GB2312)解码
function GBKdecodeURIComponent(objTag){var strResult = "";var strAry = Array.from(objTag);for(var i = 0; i < strAry.length; i ++){//判断是否中文编码字符if(strAry[i] == "%" && strAry.length - i >= 6 && strAry[3 + i] == "%"){var numByt = [];//16进制var Hex = strAry[i + 1] + strAry[i + 2];//10进制var num = parseInt(Hex, 16);numByt[0] = num;//ASCIIif(num < 0x80){strResult += String.fromCharCode(num);i += 2;}else{//16进制Hex = strAry[i + 4] + strAry[i + 5];//10进制num = parseInt(Hex, 16);numByt[1] = num;strResult += gbkToStr(numByt);i += 5}}//ASCIIelse if(strAry[i] == "%" && strAry.length - i >= 6 && strAry[3 + i] != "%"){var numByt = [];//16进制var Hex = strAry[i + 1] + strAry[i + 2];//10进制var num = parseInt(Hex, 16);numByt[0] = num;//ASCIIstrResult += String.fromCharCode(num);i += 2;}//ASCIIelse if(strAry[i] == "%" && strAry.length - i < 6){var numByt = [];//16进制var Hex = strAry[i + 1] + strAry[i + 2];//10进制var num = parseInt(Hex, 16);numByt[0] = num;//ASCIIstrResult += String.fromCharCode(num);i += 2;}else if(strAry[i] != "%"){strResult += strAry[i];}}return strResult;
}function textDecodeZxy() {
/*  var hexary = []; //16进制数组var intAry = []; //10进制整数数组var bytary = []; //字节数组
*/var decStr1 = "";var decStr2 = "";var decStr3 = "";
/*     bytary = stringToGbk('你好的说法认为yyyrr-fsdfsr123'); //[196, 227, 186, 195, 49, 50, 51]var strInput = "%BF%AA%CA%BC%CA%B1%BC%E4%BB%F2%D5%DF%BD%E1"+"%CA%F8%CA%B1%BC%E4%B8%F1%CA%BD%B4%ED%CE%F3%A3%AC%D3"+"%A6%B8%C3%CE%AAyyyy-MM-dd";decStr1 = GBKdecodeURIComponent(strInput); 
*/decStr1 = "测试数据`1234567890-=~!@#$%^&*()___+{}|:\"<>?[]\l;',.//'";decStr2 = GBKencodeURIComponent(decStr1);decStr3 = GBKdecodeURIComponent(decStr2);document.getElementById("iddecStr1").value = decStr1;document.getElementById("iddecStr2").value = decStr2;document.getElementById("iddecStr3").value = decStr3;
}
</script>