asp.net - how to validate multiple textbox for date using javascript -

the below code used validate start , end date(two textbox , date selected calendar)when button clicked.the code works fine.the problem have 8 more start , end date validate.so can tell me common code validate start , end date because of code length.

function validated() {    var cal1=document.getelementbyid('<%=enddatetwo.clientid%>').value;    var cal2= document.getelementbyid('<%=startdatetwo.clientid%>').value;          if (cal1 == '' || cal2 == '') {                 alert("start date , end date  can not bleft blank.");                 return false;             }             var dt1 = date.parse(cal1);             var dt2 = date.parse(cal2);             if (dt1 <= dt2) {                 alert("end date must occur after start date ");                 return false;             }             return true; 

i using html button call this

<asp:button id="button2"  onclientclick="return validated();" runat="server" text="enable" /> 

you create method validate(cal1, cal2) call each date pair wan tto validate within validate() method