Как я могу выбрать индекс элемента .active<li>?
<ul class = "pagination">
<li class = "paginate_button page-item previous" id = "DataTables_Table_0_previous">
<a tabindex = "0" class = "page-link" aria-controls = "DataTables_Table_0" href = "#" data-dt-idx = "0">‹</a>
</li>
<li class = "paginate_button page-item ">
<a tabindex = "0" class = "page-link" aria-controls = "DataTables_Table_0" href = "#" data-dt-idx = "1">1</a>
</li>
<li class = "paginate_button page-item active">
<a tabindex = "0" class = "page-link" aria-controls = "DataTables_Table_0" href = "#" data-dt-idx = "2">2</a>
</li>
<li class = "paginate_button page-item next disabled" id = "DataTables_Table_0_next">
<a tabindex = "0" class = "page-link" aria-controls = "DataTables_Table_0" href = "#" data-dt-idx = "3">›</a>
</li>
</ul>
Вот что я пробовал, но всегда возвращается 1:
var pageNumber = $('.pagination .page-item.active:first').index();



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Вы сказали, что хотите
...the index of the active
<li>element. If the 10th element has .active class, then I need to get9...
Функция jQuery index дает вам следующее:
var index = $("li.page-item.active").index();
Живой пример:
console.info($("li.page-item.active").index());.active {
background: yellow;
}<ul class = "pagination">
<li class = "paginate_button page-item previous" id = "DataTables_Table_0_previous">
<a tabindex = "0" class = "page-link" aria-controls = "DataTables_Table_0" href = "#" data-dt-idx = "0">‹</a>
</li>
<li class = "paginate_button page-item ">
<a tabindex = "0" class = "page-link" aria-controls = "DataTables_Table_0" href = "#" data-dt-idx = "1">1</a>
</li>
<li class = "paginate_button page-item active">
<a tabindex = "0" class = "page-link" aria-controls = "DataTables_Table_0" href = "#" data-dt-idx = "2">2</a>
</li>
<li class = "paginate_button page-item next disabled" id = "DataTables_Table_0_next">
<a tabindex = "0" class = "page-link" aria-controls = "DataTables_Table_0" href = "#" data-dt-idx = "3">›</a>
</li>
</ul>
<script src = "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>Ты имеешь в виду один из этих?
$act = $("li.active")
console.info(
$("li").index($act), // or
$act.index()
); <script src = "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<ul class = "pagination">
<li class = "paginate_button page-item previous" id = "DataTables_Table_0_previous">
<a tabindex = "0" class = "page-link" aria-controls = "DataTables_Table_0" href = "#" data-dt-idx = "0">‹</a>
</li>
<li class = "paginate_button page-item ">
<a tabindex = "0" class = "page-link" aria-controls = "DataTables_Table_0" href = "#" data-dt-idx = "1">1</a>
</li>
<li class = "paginate_button page-item active">
<a tabindex = "0" class = "page-link" aria-controls = "DataTables_Table_0" href = "#" data-dt-idx = "2">2</a>
</li>
<li class = "paginate_button page-item next disabled" id = "DataTables_Table_0_next">
<a tabindex = "0" class = "page-link" aria-controls = "DataTables_Table_0" href = "#" data-dt-idx = "3">›</a>
</li>
</ul>Эти примеры работают для меня, оба возвращают 2 для активного элемента.
console.info($('.pagination > li.active').index());//gets the index of the element relative to it's parent
console.info($('.pagination > li.active > a').data('dt-idx'));//gets the data-dt-idx value<script src = "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<ul class = "pagination">
<li class = "paginate_button page-item previous" id = "DataTables_Table_0_previous">
<a tabindex = "0" class = "page-link" aria-controls = "DataTables_Table_0" href = "#" data-dt-idx = "0">‹</a>
</li>
<li class = "paginate_button page-item ">
<a tabindex = "0" class = "page-link" aria-controls = "DataTables_Table_0" href = "#" data-dt-idx = "1">1</a>
</li>
<li class = "paginate_button page-item active">
<a tabindex = "0" class = "page-link" aria-controls = "DataTables_Table_0" href = "#" data-dt-idx = "2">2</a>
</li>
<li class = "paginate_button page-item next disabled" id = "DataTables_Table_0_next">
<a tabindex = "0" class = "page-link" aria-controls = "DataTables_Table_0" href = "#" data-dt-idx = "3">›</a>
</li>
</ul>Вы используете неправильный селектор, просто используйте:
$("ul.pagination li.active").index()
Демо:
console.info($("ul.pagination li.active").index());<script src = "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<ul class = "pagination">
<li class = "paginate_button page-item previous" id = "DataTables_Table_0_previous">
<a tabindex = "0" class = "page-link" aria-controls = "DataTables_Table_0" href = "#" data-dt-idx = "0">‹</a>
</li>
<li class = "paginate_button page-item ">
<a tabindex = "0" class = "page-link" aria-controls = "DataTables_Table_0" href = "#" data-dt-idx = "1">1</a>
</li>
<li class = "paginate_button page-item active">
<a tabindex = "0" class = "page-link" aria-controls = "DataTables_Table_0" href = "#" data-dt-idx = "2">2</a>
</li>
<li class = "paginate_button page-item next disabled" id = "DataTables_Table_0_next">
<a tabindex = "0" class = "page-link" aria-controls = "DataTables_Table_0" href = "#" data-dt-idx = "3">›</a>
</li>
</ul>