down(element[, cssRule][, index = 0]) -> HTMLElement | undefined

Returns element’s first descendant (or the n-th descendant if index is specified) that matches cssRule. If no cssRule is provided, all descendants are considered. If no descendant matches these criteria, undefined is returned.

The Element.down method is part of Prototype’s ultimate DOM traversal toolkit (check out Element.up, Element.next and Element.previous for some more Prototypish niceness). It allows precise index-based and/or CSS rule-based selection of any of the element’s descendants.

As it totally ignores text nodes (it only returns elements), you don’t have to worry about whitespace nodes.

And as an added bonus, all elements returned are already extended allowing chaining:

$(element).down(1).next('li', 2).hide();

Walking the DOM has never been that easy!

Arguments

If no argument is passed, element’s first descendant is returned (this is similar as calling firstChild except Element.down returns an already extended element.

If an index is passed, element’s corresponding descendant is returned. (This is equivalent to selecting an element from the array of elements returned by the method Element.descendants.) Note that the first element has an index of 0.

If cssRule is defined, Element.down will return the first descendant that matches it. This is a great way to grab the first item in a list for example (just pass in ‘li’ as the method’s first argument).

If both cssRule and index are defined, Element.down will collect all the descendants matching the given CSS rule and will return the one specified by the index.

In all of the above cases, if no descendant is found, undefined will be returned.

Examples

<ul id="fruits">
  <li id="apples">
    <ul>
      <li id="golden-delicious">Golden Delicious</li>
      <li id="mutsu" class="yummy">Mutsu</li>
      <li id="mcintosh" class="yummy">McIntosh</li>
      <li id="ida-red">Ida Red</li>
    </ul>
  </li>
</ul>

$('fruits').down();
// equivalent:
$('fruits').down(0);
// -> li#apple

$('fruits').down(3);
// -> li#golden-delicious

$('apples').down('li');
// -> li#golden-delicious

$('apples').down('li.yummy');
// -> li#mutsu

$('fruits').down('.yummy', 1);
// -> li#mcintosh

$('fruits').down(99);
// -> undefined