Javascript中moveElement函数为什么总是无效？

Question

照着Javascript DOM编程艺术打的，但是总是不能显示出移动的效果，我获取打印元素的位置，坐标值已经改变了，但是就是位置不移动

 function moveElement(elementID, final_x, final_y, interval) {
    if (!document.getElementById) return false;
    if (!document.getElementById(elementID)) return false;
    var elem = document.getElementById(elementID);
    if (elem.movement) {
        clearTimeout(elem.movement);
    }
    if (!elem.style.left) {
        elem.style.left = "0px";
    }
    if (!elem.style.top) {
        elem.style.top = "0px";
    }
    var xpos = parseInt(elem.style.left);
    var ypos = parseInt(elem.style.top);
    if (xpos == final_x && ypos == final_y) {
        return true;
    }
    if (xpos < final_x) {
        var dist = Math.ceil((final_x - xpos) / 10);
        xpos = xpos + dist;
    }
    if (xpos > final_x) {
        var dist = Math.ceil((xpos - final_x) / 10);
        xpos = xpos - dist;
    }
    if (ypos < final_y) {
        var dist = Math.ceil((final_y - ypos) / 10);
        ypos = ypos + dist;
    }
    if (ypos > final_y) {
        var dist = Math.ceil((ypos - final_y) / 10);
        ypos = ypos - dist;
    }
    elem.style.left = xpos + "px";
    elem.style.top = ypos + "px";
    var repeat = "moveElement('" + elementID + "'," + final_x + "," + final_y + "," + interval + ")";
    elem.movement = setTimeout(repeat.interval);
}

在另一个制作图片切换效果的例子也是，图片不移动

 function prepareSlideshow() {
    if (!document.getElementsByTagName) return false;
    if (!document.getElementById) return false;
    if (!document.getElementById("intro")) return false;
    var intro = document.getElementById("intro");
    var slideshow = document.createElement("div");
    slideshow.setAttribute("id", "slideshow");
    var preview = document.createElement("img");
    preview.setAttribute("src", "images/slideshow.jpg");
    preview.setAttribute("alt", "a glimpse of what awaits you");
    preview.setAttribute("id", "preview");
    slideshow.appendChild(preview);
    insertAfter(slideshow, intro);

    var links = intro.getElementsByTagName("a");
    var destination;
    for (var i = 0; i < links.length; i++) {
        links[i].onmouseover = function() {
            destination = this.getAttribute("href");
            if (destination.indexOf("index.html") != -1) {
                moveElement("preview, 0, 0, 5");
            }
            if (destination.indexOf("about.html") != -1) {
                moveElement("preview, -150, 0, 5");
            }
            if (destination.indexOf("photos.html") != -1) {
                moveElement("preview, -300, 0, 5");
            }
            if (destination.indexOf("live.html") != -1) {
                moveElement("preview, -450, 0, 5");
            }
            if (destination.indexOf("contact.html") != -1) {
                moveElement("preview, -600, 0, 5");
            }
        }
    }
}

Answer 1

你那个元素需要为relative或者absolute定位的设置left/top才有效，position对了没有先。。