增添和删除页面元素

 
function Button1_onclick()
{
    var divone=document.getElementById("ModifyDiv"); 
    if(!divone)
    {
        divone=document.createElement("Div");
        divone.id="ModifyDiv";
        divone.style.width="200px";
        divone.style.height="180px";
        divone.innerHTML="aaaaa"; 
        document.getElementById("aa").appendChild(divone);
    }
}
function Button2_onclick() 
{
var divone=document.getElementById("ModifyDiv"); 
if(divone){
divone.parentNode.removeChild(divone); 
} 
}
function Button3_onclick(){
alert(document.getElementById("ModifyDiv").innerHTML);
}