层的变换

 function showDiv(){
        var divClass = document.getElementById("IFdisplay");
        var divshow = document.getElementById("divshow");
        if(divClass.style.display =="none"){
            divClass.style.display ="";
            divshow.innerHTML ="- 添加条件";
        }else{
            divClass.style.display ="none";
            divshow.innerHTML ="+ 添加条件";
        }
    }