获取元素在页面上的偏移量

function getElementLeft(element) {
    var actualLeft = element.offsetLeft;
    var current = element.offsetParent;

    while (current !== null) {
        actualLeft += current.offsetLeft;
        current = current.offsetParent;
    }

    return actualLeft;
}

function getElementTop(element) {
    var actualTop = element.offsetTop;
    var current = element.offsetParent;

    while (current !== null) {
        actualTop += current.offsetTop;
        current = current.offsetParent;
    }

    return actualTop;
}