获取ListBox被选中项的JavaScript代码

function get_listBox_selection()
{
    var lb = document.getElementById("ListBox1");
    var func_ret;
    for(var i = 0; i < lb.options.length; i++)
    {
        if(lb.options[i].selected)
        {
            return i;
        }
    }
    return -1;
}