Validation for java script

var fname = document.getElementById('<%=txtFName.ClientID%>').value;
           var dob = document.getElementById('<%=txtDob.ClientID%>').value;
           var mail = document.getElementById('<%=txtMail.ClientID%>').value;
           var web = document.getElementById('<%=txtWebsite.ClientID%>').value;
           var phone = document.getElementById('<%=txtPhone.ClientID%>').value;
           var salary = document.getElementById('<%=txtSalary.ClientID%>').value;
           var department = document.getElementById('<%=drpDepart.ClientID%>').value
           var branch = document.getElementById('<%=drbBranch.ClientID%>').value
           var error = "";
           if (fname == "" && dob == "" && mail == "" && web == "" && phone == "") {

               error = "Please Enter Following Details:";

               if (fname == "") {
                   error += "\n Enter Employee FirstName.";
               }
               if (dob == "") {
                   error += "\n Enter Employee Date Of Birth.";
               }
               if (mail == "") {
                   error += "\n Enter Employee Email.";
               }
               if (web == "") {
                   error += "\n Enter Employee Website.";
               }
               if (salary == "") {
                   error += "\n Enter Employee Salary.";
               }
               if (department == "--Select--") {
                   error += "\n Select Employee Department.";
               }
               if (branch == "--Select--") {
                   error += "\n Select Employee Branch.";
               }
               alert(error);
           }
           else {
               return true;

           }