asp.net服务器控件调用js

< asp:DropDownList id = " DropDownList1 "  runat = " server " >
< asp:ListItem Value = " 1 " > 11111 </ asp:ListItem >
< asp:ListItem Value = " 2 " > 222222 </ asp:ListItem >
</ asp:DropDownList >
< div id = " div1 " > 11111 </ div >
< div id = " div2 " > 22222 </ div >

function change()
{
//下面这句使用Form1.DropDownList1.value无法得到value，要用getElementById
    if(document.getElementById ('DropDownList1').value=="1")
    {
        div2.style.display = "none";
        div1.style.display = "block";
    }
    else
    {
            div2.style.display = "block";
            div1.style.display = "none";
    } 
}

// 下面是重点，为DropDownList1控件的onChange事件绑定js的change()函数
private   void  Page_Load( object  sender, System.EventArgs e)
{
            
    DropDownList1.Attributes.Add("onChange", "change();");
}