var x=100,y=150;

function pos(dx,dy) {
    if (!document.getElementById) return;
    x += 10*dx;
    y += 10*dy;
    obj = document.getElementById("square");
    obj.style.top=y;
    obj.style.left=x;
}

function hideSquare() {
    if (!document.getElementById) return;
    obj = document.getElementById("square");
    obj.style.display="none";
}

function showSquare() {
    if (!document.getElementById) return;
    obj = document.getElementById("square");
    obj.style.display="block";
}