Operação JavaScript de adição de dias, meses, anos e semanas a datas existentes

<nome do formulário="formulário">

<TABELA>
<TR>
<TD>现在的日期：</TD>
<TD><input type="text" name="u" value="2009-01-01"></TD>
</TR>
<TR>
<TD>要加的天数：</TD>
<TD><INPUT TYPE="text" name="entry" id="d" VALUE="" onkeyup="calculate('d')"></TD>
</TR>
<TR>
<TD>要加的周数：</TD>
<TD><INPUT TYPE="text" name="entry" id="w" VALUE="" onkeyup="calculate('w')"></TD>
</TR>
<TR>
<TD>要加的月数：</TD>
<TD><INPUT TYPE="text" name="entry" id="m" VALUE="" onkeyup="calculate('m')"></TD>
</TR>
<TR>
<TD>要加的年数：</TD>
<TD><INPUT TYPE="text" name="entry" id="y" VALUE="" onkeyup="calculate('y')"></TD>
</TR>
<TR>
<TD>结果：</TD>
<TD><input name="duas vezes"></TD>
</TR>
<!--<TR>
<TD>要加的日期2：</TD>
<TD><input type="text" name="u" value="2009/01/01"></TD>
</TR>
<TR>
<TD>结果2：</TD>
<TD><input name="duas vezes"></TD>
</TR>-->
</TABELA>
</form>
<linguagem script="JavaScript">
function DateAdd(strInterval, NumDay, dtDate) {
var dtTmp = nova Data(dtData);
if (isNaN(dtTmp)) dtTmp = new Date();
switch (strInterval) {
caso "s":
dtTmp = new Date(Date.parse(dtTmp) + (1000 * parseInt(NumDay)));
quebrar;
caso "n":
dtTmp = new Date(Date.parse(dtTmp) + (60000 * parseInt(NumDay)));
quebrar;
caso "h":
dtTmp = new Date(Date.parse(dtTmp) + (3600000 * parseInt(NumDay)));
quebrar;
caso "d":
dtTmp = new Date(Date.parse(dtTmp) + (86400000 * parseInt(NumDay)));
quebrar;
caso "w":
dtTmp = new Date(Date.parse(dtTmp) + ((86400000 * 7) * parseInt(NumDay)));
quebrar;
caso "m":
dtTmp = nova Data(dtTmp.getFullYear(), (dtTmp.getMonth())+parseInt(NumDay), dtTmp.getDate(), dtTmp.getHours(), dtTmp.getMinutes(), dtTmp.getSeconds());
quebrar;
caso "y":
//alert(dtTmp.getFullYear());
dtTmp = nova Data(dtTmp.getFullYear()+parseInt(NumDay), dtTmp.getMonth(), dtTmp.getDate(), dtTmp.getHours(), dtTmp.getMinutes(), dtTmp.getSeconds());
//alerta(dtTmp);
quebrar;
}
var mStr=new String(dtTmp.getMonth()+1);
var dStr=new String(dtTmp.getDate());
if (mStr.comprimento==1){
mStr="0"+mStr;
}
if (dStr.comprimento==1){
dStr="0"+dStr;
}
return dtTmp.getFullYear()+"-"+mStr+"-"+dStr;
}
</script>
<script language="JavaScript">

função calcular(tipo)
{
var entrada = document.getElementById(type).value;//自己判断是否合法
var uValue=document.form.u.value;
uValue=uValue.replace("-","/").replace("-","/");
//alerta(uValor);
document.form.twice.value = DateAdd(tipo,entrada,uValor);
}
</script>