字符串base64与二进制互转（兼容ie8）

function stringToByte(str) {
    var bytes = new Array();
    var len, c;
    len = str.length;
    for (var i = 0; i < len; i++) {
        c = str.charCodeAt(i);
        if (c >= 0x010000 && c <= 0x10FFFF) {
            bytes.push(((c >> 18) & 0x07) | 0xF0);
            bytes.push(((c >> 12) & 0x3F) | 0x80);
            bytes.push(((c >> 6) & 0x3F) | 0x80);
            bytes.push((c & 0x3F) | 0x80);
        } else if (c >= 0x000800 && c <= 0x00FFFF) {
            bytes.push(((c >> 12) & 0x0F) | 0xE0);
            bytes.push(((c >> 6) & 0x3F) | 0x80);
            bytes.push((c & 0x3F) | 0x80);
        } else if (c >= 0x000080 && c <= 0x0007FF) {
            bytes.push(((c >> 6) & 0x1F) | 0xC0);
            bytes.push((c & 0x3F) | 0x80);
        } else {
            bytes.push(c & 0xFF);
        }
    }
    return bytes;


}

function utf8ByteToUnicodeStr(utf8Bytes){
    var unicodeStr ="";
    for (var pos = 0; pos < utf8Bytes.length;){
        var flag= utf8Bytes[pos];
        var unicode = 0 ;
        if ((flag >>>7) === 0 ) {
            unicodeStr+= String.fromCharCode(utf8Bytes[pos]);
            pos += 1;

        } else if ((flag &0xFC) === 0xFC ){
            unicode = (utf8Bytes[pos] & 0x3) << 30;
            unicode |= (utf8Bytes[pos+1] & 0x3F) << 24;
            unicode |= (utf8Bytes[pos+2] & 0x3F) << 18;
            unicode |= (utf8Bytes[pos+3] & 0x3F) << 12;
            unicode |= (utf8Bytes[pos+4] & 0x3F) << 6;
            unicode |= (utf8Bytes[pos+5] & 0x3F);
            unicodeStr+= String.fromCharCode(unicode) ;
            pos += 6;

        }else if ((flag &0xF8) === 0xF8 ){
            unicode = (utf8Bytes[pos] & 0x7) << 24;
            unicode |= (utf8Bytes[pos+1] & 0x3F) << 18;
            unicode |= (utf8Bytes[pos+2] & 0x3F) << 12;
            unicode |= (utf8Bytes[pos+3] & 0x3F) << 6;
            unicode |= (utf8Bytes[pos+4] & 0x3F);
            unicodeStr+= String.fromCharCode(unicode) ;
            pos += 5;

        } else if ((flag &0xF0) === 0xF0 ){
            unicode = (utf8Bytes[pos] & 0xF) << 18;
            unicode |= (utf8Bytes[pos+1] & 0x3F) << 12;
            unicode |= (utf8Bytes[pos+2] & 0x3F) << 6;
            unicode |= (utf8Bytes[pos+3] & 0x3F);
            unicodeStr+= String.fromCharCode(unicode) ;
            pos += 4;

        } else if ((flag &0xE0) === 0xE0 ){
            unicode = (utf8Bytes[pos] & 0x1F) << 12;;
            unicode |= (utf8Bytes[pos+1] & 0x3F) << 6;
            unicode |= (utf8Bytes[pos+2] & 0x3F);
            unicodeStr+= String.fromCharCode(unicode) ;
            pos += 3;

        } else if ((flag &0xC0) === 0xC0 ){ //110
            unicode = (utf8Bytes[pos] & 0x3F) << 6;
            unicode |= (utf8Bytes[pos+1] & 0x3F);
            unicodeStr+= String.fromCharCode(unicode) ;
            pos += 2;

        } else{
            unicodeStr+= String.fromCharCode(utf8Bytes[pos]);
            pos += 1;
        }
    }
    return unicodeStr;
}
console.log("base64转字节流",stringToByte('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'))
// base64转字节流 [47, 57, 106, 47, 52, 65, 65, 81, 83, 107, 90, 74, 82, 103, 65, 66, 65, 81, 65, 65, 65, 81, 65, 66, 65, 65, 68, 47, 50, 119, 66, 68, 65, 65, 69, 66, 65, 81, 69, 66, 65, 81, 69, 66, 65, 81, 69, 66, 65, 81, 69, 66, 65, 81, 69, 66, 65, 81, 69, 66, 65, 81, 69, 66, 65, 81, 69, 66, 65, 81, 69, 66, 65, 81, 69, 66, 65, 81, 69, 66, 65, 81, 69, 66, 65, 81, 69, 66, 65, 81, 69, 66, 65, 81, 69, 66, 65, 81, 69, 66, …]
const bytesArr = stringToByte('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')
console.log('字节流转字符串',utf8ByteToUnicodeStr(bytesArr))
// 字节流转字符串 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