How to input byte array to a function?

Question

I have a function in my contract and it have bytes1[4] array parameter and returns.

function foo(bytes1[4] memory _mdata) public pure returns(bytes1[4]){
    bytes1[4] memory result;
    uint8 i;
    for(i=0 ; i<4 ; i++){
        result[i] = _mdata[i];
    }
    return result;
}

And in my truffle test javascript, it have something like..

var myData = [0x01, 0x02, 0x03, 0x1f];
it("test", async() => {
    let instant = await myArithmetic.deployed();
    let result = await instant.foo(myData);
    console.log(result);

I got [ '0x10', '0x20', '0x30', '0x1f' ] Is this because of different endian between javascript and solidty compiler? But why the last one returned correctly??