transform + reduce

index.js

function readPosX(stream, acc) {
    let val = stream.substr(0, 2);
    acc.posX = val;
    return stream.substr(2);
}

function readPosY(stream, acc) {
    let val = stream.substr(0, 2);
    acc.posY = val;
    return stream.substr(2);
}

var transformations = [readPosX, readPosY];

var stream = 'abcdef';
var data = {};
transformations.forEach(func => {
    stream = func(stream, data);
});