一个简单的js

function ShowMenu(Menu1) {
    if (ShowID == Menu1) {
        Menu1 = 0;
        ShowID = 0;
    }
    for (var i = 1; i <= 20; i++) {
        if (i == 18) continue;
        if (i == Menu1) { //如果是当前大类
            var objArr = eval("document.all.pad" + i);
            count = objArr.length;
            //var count = (document.all.pad + "i").length;
            if ( count == null) { //如果只有一个子类
                //var obj = eval("document.all.pad" + i);
                objArr.style.display='block';
            } 
            else { //如果多个子类
                for (var j = 0; j < count; j++) {
                    //var obj = eval("document.all.pad" + i);
                    objArr[j].style.display='block'; //用下标的方式
                }
            }
            MM_swapImage('image' + i, '', 'sec_26.gif', 0); //替换箭头图标
            ShowID = Menu1
        } else { //如果不是当前大类
            var objArr = eval("document.all.pad" + i);
            count = objArr.length;
            if (count == null) {
                //var obj = eval("document.all.pad" + i);
                objArr.style.display='none';
            } else {
                for (var j = 0; j < count; j++) {
                    //var obj = eval("document.all.pad" + i);
                    objArr[j].style.display='none';
                }
            }
            MM_swapImage('image' + i, '', 'sec_32.gif', 0); //替换箭头图标
        }
    }
}