在 JavaScript 中的个位数月份和日期之前添加零 (MM/DD/YYYY）

function validateContact() {
       <%-- var summary = "";
        summary+=CheckForEmpty('<%=txtName.ClientID%>',"");--%>
        var msg = "";
        var count = 0;
        var contactname = document.getElementById('<%=txtName.ClientID%>').value;
        var alphaExp = /^[A-Za-z0-9 ]{3,20}$/;
        if (contactname.trim().length == 0 || contactname == "" || contactname == null || !contactname.match(alphaExp)) {
            count++;
            msg += count + " Enter First Name 'n";
        }
        var lastname = document.getElementById('<%=txtName2.ClientID%>').value;
        var alphaExp = /^[A-Za-z0-9 ]{3,20}$/;
        if (lastname.trim().length == 0 || lastname == "" || lastname == null ) {
            count++;
            msg += count + " Enter Last Name 'n";
        }
        var ct_company = document.getElementById('<%=txt_cp_company.ClientID%>').value;
        if (ct_company.length == 0 || ct_company == "" || ct_company == null) {
            count++;
            msg += count + " Enter Company Name 'n";
        }
        var designation = document.getElementById('<%=txtDesignation.ClientID%>').value;
    var alphaExp = /^[A-Za-z0-9 ]{2,30}$/;
    if (designation.trim().length == 0 || designation == "" || designation == null ) {
        count++;
        msg += count + " Enter Designation  'n";
    }
    var emailid = document.getElementById('<%=txtEmailId.ClientID%>').value;
        var regxEmailID = /^(['w-'.]+)@(('[[0-9]{1,3}'.[0-9]{1,3}'.[0-9]{1,3}'.)|((['w-]+'.)+))([a-zA-Z]{2,4}|[0-9]{1,3})(']?)$/;
        //var regxEmailID = /^([a-zA-Z0-9_'.'a-zA-Z0-9])+'@(([a-zA-Z0-9'-])+'.)+([a-zA-Z0-9]{2,4})+$/;
    if (emailid.trim().length == 0 || emailid == "" || emailid == null) {
        count++;
        msg += count + " Enter Email-Id  'n";
    }
    else if (!emailid.match(regxEmailID)) {
        count++;
        msg += count + "Enter Valid Email-Id  'n";
    }
    var address = document.getElementById('<%=txt_cp_address.ClientID%>').value;
    var alphaExp = /^[A-Za-z0-9 ]{3,20}$/;
    if (address.trim().length == 0 || address == "" || address == null ) {
        count++;
        msg += count + " Enter Address 'n";
    }

    var mobno = document.getElementById('<%=txtMobile.ClientID %>').value;
      var MobExp = /^([0-9])+$/;
      if (mobno == "" || mobno.length != 10) {
          count++;
          msg += count + " Enter Mobile No  'n";
      }
      else if (!mobno.match(MobExp)) {
          count++;
          msg += count + "Enter Valid Mobile No 'n";
      }
      var dob = document.getElementById('<%=txt_dob.ClientID%>').value;
      var re = /^'d{1,2}'/'d{1,2}'/'d{4}$/;
        if (dob =="MM/DD/YYYY")
        {
            document.getElementById('<%=txt_dob.ClientID%>').value = "";
        }
        else if (!dob.match(re)) {
            count++;
            msg += count + " InValid date of birth 'n";
        }
        else {
            var datestring = dob.replace(new RegExp("/", "g"), '');
            if (datestring.substring(0, 2) < 1 || datestring.substring(0, 2) > 12) {
                count++;
                msg += count + " You've entered incorrect month 'n";
            }
            if (datestring.substring(2, 4) < 1 || datestring.substring(2, 4) > 31) {
                count++;
                msg += count + " You've entered incorrect date 'n";
            }
        }

      if (document.getElementById('<%=rbtn_yes.ClientID%>').checked == false && document.getElementById('<%=rbtn_no.ClientID%>').checked == false) {
          count++;
          msg += count + " Enter Decision Maker 'n";
      }           
      if (msg.toString() == "") {
      }
      else {
          alert(msg);
          return false;
      }

  }

如果月份或日期为个位数，我想用零填充。此代码不接受个位数的月份和日期，如果我输入 08/08/2015，它应该看起来像这样 08/08/2015。