javascript控制页面控件显示不显示

function Checkbox1_onclick() {
var CheckboxStartDate = document.getElementById("CheckboxStartDate").checked;
取得html控件

//var aa = document.getElementById("ctl00_mainContent_tdDdlStartHour");

取得服务器控件
if(CheckboxStartDate == true)
{
alert(CheckboxStartDate);
}
else
{
var tdDdlStartHour = document.getElementById("ctl00_mainContent_tdDdlStartHour");
if (tdDdlStartHour.style.display == "none")
{
tdDdlStartHour.style.display = "block";
}
else
{
tdDdlStartHour.style.display = "none";
}

}
}