オブジェクトの順番をイントラクティブに操作させてくえるjQuery UIに含まれるSortableの紹介。　

Sortableのページ
https://api.jqueryui.com/sortable/

APIの詳細
https://api.jqueryui.com/sortable/

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>jQuery UI Sortable - Default functionality</title>
  <link rel="stylesheet" href="//code.jquery.com/ui/1.12.1/themes/base/jquery-ui.css">
  <link rel="stylesheet" href="/resources/demos/style.css">
  <style>
  #sortable { list-style-type: none; margin: 0; padding: 0; width: 60%; }
  #sortable li { margin: 0 3px 3px 3px; padding: 0.4em; padding-left: 1.5em; font-size: 1.4em; height: 18px; }
  #sortable li span { position: absolute; margin-left: -1.3em; }
  </style>
  <script src="https://code.jquery.com/jquery-1.12.4.js"></script>
  <script src="https://code.jquery.com/ui/1.12.1/jquery-ui.js"></script>
  <script>
  $( function() {
    $( "#sortable" ).sortable();
    $( "#sortable" ).disableSelection();
  } );
  </script>
</head>
<body>
 
<ul id="sortable">
  <li class="ui-state-default"><span class="ui-icon ui-icon-arrowthick-2-n-s"></span>Item 1</li>
  <li class="ui-state-default"><span class="ui-icon ui-icon-arrowthick-2-n-s"></span>Item 2</li>
  <li class="ui-state-default"><span class="ui-icon ui-icon-arrowthick-2-n-s"></span>Item 3</li>
  <li class="ui-state-default"><span class="ui-icon ui-icon-arrowthick-2-n-s"></span>Item 4</li>
  <li class="ui-state-default"><span class="ui-icon ui-icon-arrowthick-2-n-s"></span>Item 5</li>
  <li class="ui-state-default"><span class="ui-icon ui-icon-arrowthick-2-n-s"></span>Item 6</li>
  <li class="ui-state-default"><span class="ui-icon ui-icon-arrowthick-2-n-s"></span>Item 7</li>
</ul>
 
 
</body>
</html>

順番を変更したら、新しいポジションを知りたい。そんな時は。

<script src="https://code.jquery.com/ui/1.12.1/jquery-ui.js"></script>
  <script>
    $(function () {
      $("#sortable").sortable({
        start: function (event, ui) {
          ui.item.startPos = ui.item.index();
        },
        stop: function (event, ui) {
          alert("Moved from " + ui.item.startPos + " to " + ui.item.index());
        }
      });
    $("#sortable").disableSelection();
  });
</script>