Converting javascript Integer to byte array and back

Using the hint provided by Susanoh13, here are the two functions that allow conversion of number from/to ByteArray:

longToByteArray = function(/*long*/long) {
    // we want to represent the input as a 8-bytes array
    var byteArray = [0, 0, 0, 0, 0, 0, 0, 0];

    for ( var index = 0; index < byteArray.length; index ++ ) {
        var byte = long & 0xff;
        byteArray [ index ] = byte;
        long = (long - byte) / 256 ;
    }

    return byteArray;
};

byteArrayToLong = function(/*byte[]*/byteArray) {
    var value = 0;
    for ( var i = byteArray.length - 1; i >= 0; i--) {
        value = (value * 256) + byteArray[i];
    }

    return value;
};