Given a jQuery object that represents a set of DOM elements, the .find() method allows us to search through the descendants of these elements in the DOM tree and construct a new jQuery object from the matching elements. The .find() and .children() methods are similar, except that the latter only travels a single level down the DOM tree.

The first signature for the .find()method accepts a selector expression of the same type that we can pass to the $() function. The elements will be filtered by testing whether they match this selector.

Consider a page with a basic nested list on it:

<ul class="level-1">
  <li class="item-i">I</li>
  <li class="item-ii">II
    <ul class="level-2">
      <li class="item-a">A</li>
      <li class="item-b">B
        <ul class="level-3">
          <li class="item-1">1</li>
          <li class="item-2">2</li>
          <li class="item-3">3</li>
        </ul>
      </li>
      <li class="item-c">C</li>
    </ul>
  </li>
  <li class="item-iii">III</li>
</ul>

If we begin at item II, we can find list items within it:

$('li.item-ii').find('li').css('background-color', 'red');

The result of this call is a red background on items A, B, 1, 2, 3, and C. Even though item II matches the selector expression, it is not included in the results; only descendants are considered candidates for the match.

Unlike in the rest of the tree traversal methods, the selector expression is required in a call to .find(). If we need to retrieve all of the descendant elements, we can pass in the universal selector '*' to accomplish this.

Selector context is implemented with the .find() method; therefore, $('li.item-ii').find('li') is equivalent to $('li', 'li.item-ii').

As of jQuery 1.6, we can also filter the selection with a given jQuery collection or element. With the same nested list as above, if we start with:

var $allListElements = $('li');

And then pass this jQuery object to find:

$('li.item-ii').find( $allListElements );

This will return a jQuery collection which contains only the list elements that are descendants of item II.

Similarly, an element may also be passed to find:

var item1 = $('li.item-1')[0];
$('li.item-ii').find( item1 ).css('background-color', 'red');

The result of this call would be a red background on item 1.