javascript – 检测网页,下拉菜单是否会显示在屏幕外

我有一个基于CSS的简单下拉菜单,有多个级别.第二级或第三级可能超出可见窗口,具有分辨率和窗口大小的某些组合.

如果检测到这种情况,一些预先构建的菜单控件只会打开向左而不是向右的下拉菜单.

我如何测试(使用JS / jQuery)这种情况？

解决方法:

您可以使用以下功能测试菜单项是否在屏幕外：

/*---   function bIsNodeClippedOrOffscreen returns true if a node
        is offscreen (without scrolling).
        Requires jQuery.
*/
function bIsNodeClippedOrOffscreen (zJnode)
{
    var aDivPos             = zJnode.offset ();
    var iLeftPos            = aDivPos.left;
    var iTopPos             = aDivPos.top;

    var iDivWidth           = zJnode.outerWidth  (true);
    var iDivHeight          = zJnode.outerHeight (true);

    var bOffScreen          = CheckIfPointIsOffScreen (iLeftPos, iTopPos);
    var bClipped            = CheckIfPointIsOffScreen (iLeftPos + iDivWidth, iTopPos + iDivHeight);

    return (bOffScreen || bClipped);
}


function CheckIfPointIsOffScreen (iLeftPos, iTopPos)
{
    var ibrowserWidth       = $(window).width()  - 16;   //-- 16 is fudge for scrollbars, refine later
    var ibrowserHeight      = $(window).height() - 16;   //-- 16 is fudge for scrollbars, refine later
    var bOffScreen          = false;

    if (iLeftPos < 0  ||  iLeftPos >= ibrowserWidth)
        bOffScreen          = true;

    if (iTopPos < 0   ||  iTopPos >= ibrowserHeight)
        bOffScreen          = true;

    return bOffScreen;
}

.
样品用法：

<li id="SomeMenuItem"> Get your shopping cart for free!
...
...

var Node            = $("#SomeMenuItem");

var NeedToMoveIt    = bIsNodeClippedOrOffscreen (Node);