Same code behave differently on two servers

Question

In my localhost and one server is all right, array has the same values within console inside $.each function like outside, but on another server that code behave differently. Second console return empty array, inside it is correct. How can server change client-side language behaviour?

var isChecked = [];
$('.x').each(function() {
  if ($(this).prop('checked')) {
    id = $(this).prop('id').split('_')[1];
    isChecked.push(id);
    console.log(isChecked);
  } else {
    isChecked.splice($.inArray(id, isChecked), 1);
  }
});
console.log(isChecked);

Markup is:

<table>
  <tr class=header>
    <td class=first>
      <input type="checkbox" id="c">
      <label for="c"><span class="tablecheck"></span></label>
    </td>
    <td class="header" colspan=""><a href="/">User group</a></td>
    <td class="header" colspan=""><a href="/">Firstname</a></td>
    <td class="header" colspan="2"><a href="/">Lastname</a></td>
  </tr>
  <tr class="">
    <td class=first>
      <input type="checkbox" id="x_41" class="x">
      <label for="x_41"><span class="tablecheck"></span></label>
    </td>
    <td>Admin</td>
    <td>Firstname</td>
    <td>Lastname</td>
  </tr>
</table>

Answer 1

How can server change client-side language behaviour?

I would guess your browser has cached an older version of the JavaScript file from the second server, which would explain why you are seeing different behavior.