js中截取无特殊符号的字符串和取得特殊时间

function onChangeType()
{
today = new Date();
var todayStr = today.getYear();
if(today.getMonth()<10){
todayStr=todayStr+"0"+(today.getMonth()+1);<%--加1转换为本地月份,如果月份小于10，就在前面加0补成双位数,日期一样--%>
}
else{
todayStr=todayStr+(today.getMonth()+1);
}

if(today.getDate()<10){
todayStr=todayStr+"0"+today.getDate();
}
else{
todayStr=todayStr+today.getDate();
}
alert(todayStr);
var typeName=document.getElementById("dtype").value;
var lipinid=document.getElementById("presentid").value;
var length1=document.getElementById("presentid").value.length;

lipinid=lipinid.substring(length1-3,length1);<%--每次截取礼品编号的最后三位，也就是最初生成的序列号--%>
var presentid=(typeName+lipinid);<%--把截取的字符串加上下拉框选中的值,拼成新的礼品编号--%>
document.getElementById("presentid").value=(todayStr+presentid);<%--重新赋值--%>

}