:nth-child Selector

nth-child selector

version added: 1.1.4jQuery(':nth-child(index/even/odd/equation)')

  • index
    The index of each child to match, starting with 1, the string even or odd, or an equation ( eg. :nth-child(even), :nth-child(4n) )

Description: Selects all elements that are the nth-child of their parent.

Because jQuery's implementation of :nth-child(n) is strictly derived from the CSS specification, the value of n is "1-indexed", meaning that the counting starts at 1. For all other selector expressions, however, jQuery follows JavaScript's "0-indexed" counting. Therefore, given a single <ul> containing two <li>s, $('li:nth-child(1)') selects the first <li> while $('li:eq(1)') selects the second.

The :nth-child(n) pseudo-class is easily confused with :eq(n), even though the two can result in dramatically different matched elements. With :nth-child(n), all children are counted, regardless of what they are, and the specified element is selected only if it matches the selector attached to the pseudo-class. With :eq(n) only the selector attached to the pseudo-class is counted, not limited to children of any other element, and the nth one is selected.

Further discussion of this unusual usage can be found in the W3C CSS specification.

Examples:

Example: Finds the second li in each matched ul and notes it. 

<!DOCTYPE html>
<html>
<head>
  <style>

  div { float:left; }
  span { color:blue; }
  </style>
  <script src="https://code.jquery.com/jquery-latest.js"></script>
</head>
<body>
	<div><ul>
    <li>John</li>
    <li>Karl</li>
    <li>Brandon</li>

  </ul></div>
  <div><ul>
    <li>Sam</li>
  </ul></div>

  <div><ul>
    <li>Glen</li>
    <li>Tane</li>
    <li>Ralph</li>

    <li>David</li>
  </ul></div>
<script>$("ul li:nth-child(2)").append("<span> - 2nd!</span>");</script>
</body>
</html>

Demo:

Example: This is a playground to see how the selector works with different strings. Notice that this is different from the :even and :odd which have no regard for parent and just filter the list of elements to every other one. The :nth-child, however, counts the index of the child to its particular parent. In any case, it's easier to see than explain so... 

<!DOCTYPE html>
<html>
<head>
  <style>
  button { display:block; font-size:12px; width:100px; }
  div { float:left; margin:10px; font-size:10px;
        border:1px solid black; }
  span { color:blue; font-size:18px; }
  #inner { color:red; }
  td { width:50px; text-align:center; }
  </style>
  <script src="https://code.jquery.com/jquery-latest.js"></script>
</head>
<body>
	<div>
    <button>:nth-child(even)</button>
    <button>:nth-child(odd)</button>
    <button>:nth-child(3n)</button>

    <button>:nth-child(2)</button>
  </div>
  <div>
    <button>:nth-child(3n+1)</button>
    <button>:nth-child(3n+2)</button>

    <button>:even</button>
    <button>:odd</button>
  </div>
  <div><table>

    <tr><td>John</td></tr>
    <tr><td>Karl</td></tr>
    <tr><td>Brandon</td></tr>

    <tr><td>Benjamin</td></tr>
  </table></div>
  <div><table>
    <tr><td>Sam</td></tr>

  </table></div>
  <div><table>
    <tr><td>Glen</td></tr>
    <tr><td>Tane</td></tr>

    <tr><td>Ralph</td></tr>
    <tr><td>David</td></tr>
    <tr><td>Mike</td></tr>

    <tr><td>Dan</td></tr>
  </table></div>
  <span>
    tr<span id="inner"></span>

  </span>
<script>
    $("button").click(function () {
      var str = $(this).text();
      $("tr").css("background", "white");
      $("tr" + str).css("background", "#ff0000");
      $("#inner").text(str);
    });

</script>
</body>
</html>

Demo: