Given a jQuery object that represents a set of DOM elements, the .eq() method constructs a new jQuery object from one element within that set. The supplied index identifies the position of this element in the set.

Consider a page with a simple list on it:

  <ul>
    <li>list item 1</li>
    <li>list item 2</li>
    <li>list item 3</li>
    <li>list item 4</li>
    <li>list item 5</li>
  </ul>

We can apply this method to the set of list items:

  $('li').eq(2).css('background-color', 'red');

The result of this call is a red background for item 3. Note that the supplied index is zero-based, and refers to the position of the element within the jQuery object, not within the DOM tree.

Providing a negative number indicates a position starting from the end of the set, rather than the beginning. For example:

  $('li').eq(-2).css('background-color', 'red');

This time list item 4 is turned red, since it is two from the end of the set.

If an element cannot be found at the specified zero-based index, the method constructs a new jQuery object with an empty set and a length property of 0.

  $('li').eq(5).css('background-color', 'red');

Here, none of the list items is turned red, since .eq(5) indicates the sixth of five list items.