Datepicker javascript - Cannot read property 'valueOf'

i want to use datepicekr as check-in - check-out so I have HTML:

<!-- Text input-->
<div class="form-group">
  <label class="col-md-4 control-label" for="datum">Datum: Od</label>  
  <div class="col-md-3">
<input id="dp1" name="dp1" class="form-control" placeholder="Datum" type="text">
  </div>
  <div class="col-md-3">
<input id="dp2" name="dp2" class="form-control" placeholder="Datum" type="text">
  </div>
</div>

I try to make it workable with js:

var nowTemp = new Date();
var now = new Date(nowTemp.getFullYear(), nowTemp.getMonth(), nowTemp.getDate(), 0, 0, 0, 0);
 
var checkin = $("#dp1").datepicker({
  onRender: function(date) {
    return date.valueOf() < now.valueOf() ? 'disabled' : '';
  }
}).on('changeDate', function(ev) {
  if (ev.date.valueOf() > checkout.date.valueOf()) {
    var newDate = new Date(ev.date)
    newDate.setDate(newDate.getDate() + 1);
    checkout.setValue(newDate);
  }
  checkin.hide();
  $("#dp2")[0].focus();
}).data('datepicker');
var checkout = $("#dp2").datepicker({
  onRender: function(date) {
    return date.valueOf() <= checkin.date.valueOf() ? 'disabled' : '';
  }
}).on('changeDate', function(ev) {
  checkout.hide();
}).data('datepicker');

but I get error:

Uncaught TypeError: Cannot read property 'valueOf' of undefined 

What that exactly mean? What I can do to solve this problem? I use the code from official web resource for datepicker for bootstrap...

The javascript is working fine based off the example provided on the project page.

The only thing I can think of is that Javascript library is not loading.
Try adding the following lines of code to your web page (or their local equivalants)

<link rel="stylesheet" type="text/css" href="http://kylemitofsky.com/libraries/libraries/datepicker.css">
<script type="text/javascript" src="http://kylemitofsky.com/libraries/libraries/bootstrap-datepicker.js"></script>

Working Demo in Fiddle

If this doesn't work for you, try using the fiddle as a launching off point to ask more targeted questions in the future.