Skip32 javascript endianness issue

Question

I wanted to "quickly" try out a skip32 implementation in a form "client script" in ERPNext (javascript) and ended up with code like this:

frappe.web_form.validate = () => {
    console.log('formname frappe.web_form.validate()');
    data = frappe.web_form.get_values(); 
    var cipher = new Skip32('s3cr3t k3y');
    var enc = cipher.encrypt(42);
    console.log('enc ' + value + ':' + enc);
    var dec = cipher.decrypt(enc);
    console.log('dec ' + value + ':' + dec);

... (frappe code) ...
};

function Skip32(key) {
    this.key = new Uint8Array(10);
    for (var i = 0; i < 10; i++) this.key[i] = key.charCodeAt(i % key.length);

// var _buf = new Buffer([
var ftable = new Uint8Array([
0xa3,0xd7,0x09,0x83,0xf8,0x48,0xf6,0xf4,0xb3,0x21,0x15,0x78,0x99,0xb1,0xaf,0xf9,
0xe7,0x2d,0x4d,0x8a,0xce,0x4c,0xca,0x2e,0x52,0x95,0xd9,0x1e,0x4e,0x38,0x44,0x28,
0x0a,0xdf,0x02,0xa0,0x17,0xf1,0x60,0x68,0x12,0xb7,0x7a,0xc3,0xe9,0xfa,0x3d,0x53,
0x96,0x84,0x6b,0xba,0xf2,0x63,0x9a,0x19,0x7c,0xae,0xe5,0xf5,0xf7,0x16,0x6a,0xa2,
0x39,0xb6,0x7b,0x0f,0xc1,0x93,0x81,0x1b,0xee,0xb4,0x1a,0xea,0xd0,0x91,0x2f,0xb8,
0x55,0xb9,0xda,0x85,0x3f,0x41,0xbf,0xe0,0x5a,0x58,0x80,0x5f,0x66,0x0b,0xd8,0x90,
0x35,0xd5,0xc0,0xa7,0x33,0x06,0x65,0x69,0x45,0x00,0x94,0x56,0x6d,0x98,0x9b,0x76,
0x97,0xfc,0xb2,0xc2,0xb0,0xfe,0xdb,0x20,0xe1,0xeb,0xd6,0xe4,0xdd,0x47,0x4a,0x1d,
0x42,0xed,0x9e,0x6e,0x49,0x3c,0xcd,0x43,0x27,0xd2,0x07,0xd4,0xde,0xc7,0x67,0x18,
0x89,0xcb,0x30,0x1f,0x8d,0xc6,0x8f,0xaa,0xc8,0x74,0xdc,0xc9,0x5d,0x5c,0x31,0xa4,
0x70,0x88,0x61,0x2c,0x9f,0x0d,0x2b,0x87,0x50,0x82,0x54,0x64,0x26,0x7d,0x03,0x40,
0x34,0x4b,0x1c,0x73,0xd1,0xc4,0xfd,0x3b,0xcc,0xfb,0x7f,0xab,0xe6,0x3e,0x5b,0xa5,
0xad,0x04,0x23,0x9c,0x14,0x51,0x22,0xf0,0x29,0x79,0x71,0x7e,0xff,0x8c,0x0e,0xe2,
0x0c,0xef,0xbc,0x72,0x75,0x6f,0x37,0xa1,0xec,0xd3,0x8e,0x62,0x8b,0x86,0x10,0xe8,
0x08,0x77,0x11,0xbe,0x92,0x4f,0x24,0xc5,0x32,0x36,0x9d,0xcf,0xf3,0xa6,0xbb,0xac,
0x5e,0x6c,0xa9,0x13,0x57,0x25,0xb5,0xe3,0xbd,0xa8,0x3a,0x01,0x05,0x59,0x2a,0x46,
]);
//var ftable = new Uint8Array(_buf);

this.round16 = function(k, n){
    var g1, g2, g3, g4, g5, g6;
    g1 = (n>>8) & 0xff;
    g2 = (n>>0) & 0xff;
    g3 = ftable[g2^this.key[(4*k+0)%10]] ^ g1;
    g4 = ftable[g3^this.key[(4*k+1)%10]] ^ g2;
    g5 = ftable[g4^this.key[(4*k+2)%10]] ^ g3;
    g6 = ftable[g5^this.key[(4*k+3)%10]] ^ g4;
    return (g5<<8)+g6;
}

this.core = function(n,k,d){
    var i, k, wl, wr;
    wl = (((n>>24) & 0xff)<<8) + (((n>>16) & 0xff)<<0);
    wr = (((n>>8) & 0xff)<<8) + (((n>>0) & 0xff)<<0);
    for(i=0;i<24/2;i++){
        wr ^= this.round16(k, wl) ^ k;
        k+=d;
        wl ^= this.round16(k, wr) ^ k;
        k+=d;
    }
    return ((wr << 16) | wl)>>>0;
}

this.encrypt = function(n){
    return this.core(n,0,1);
}

this.decrypt = function(n){
    return this.core(n,23,-1);
}

this.checkEndian = function() {
    var arrayBuffer = new ArrayBuffer(2);
    var uint8Array = new Uint8Array(arrayBuffer);
    var uint16array = new Uint16Array(arrayBuffer);
    uint8Array[0] = 0xAA; // set first byte
    uint8Array[1] = 0xBB; // set second byte
    if(uint16array[0] === 0xBBAA) return "little endian";
    if(uint16array[0] === 0xAABB) return "big endian";
    else throw new Error("Something crazy just happened");
}
}

The skip32 code is adapted from this Node module source file: https://github.com/femto113/node-skip32/blob/master/skip32.js

This code worked in as much as it would encrypt then decrypt back to the original value. To confirm the ability to decode data generated on a different system (in Python3 using the "skippy" library) I first attempted to use the unit test data from https://github.com/pyrige/skippy/blob/master/skippy/tests/test_skippy.py which uses the key: b"s3cr3t k3y" and a test value of 42 but the expected result depends on whether the endianness of the host system being "little" or "big":

class SkippyTest(unittest.TestCase):
    if sys.byteorder == "little":
        test_data = {42: 2444721374, 4711: 3970196332,
                     935425436: 42, 798322584: 4711}
    else:
        test_data = {42: 406043987, 4711: 4097152607,
                     935425436: 2123491105, 798322584: 2445249305}

When I try to validate the javascript code using that key and the value 42 it generates 406043987 i.e. the "big-endian" expected result not 2444721374. Hence I added the "endian" test function and sure enough it gives the endianness as "little".

Both the Python and Javascript systems are Intel Core (so little-endian) and running the Python code with those test values generates the expected little-endian result 2444721374.

NB: ERPNext/Frappe seems to be irrelevant here (unsurprisingly) - entering the Skip32 function code directly at a web browser javascript console yields the same outcome.

Can anyone explain the anomalous result from this javascript code?