javascript - jQuery "hasParent"

Question

The JQuery "has" method effectively selects all elements where they have particular descendants.

I want to select elements based on the fact they have particular ancestors. I know about parent([selector]) and parents([selector]) but these select the parents and not the children with the parents.

So is there an ancestor equivalent of "has"?

Note: I already have the context of an element further down the hierarchy and I will be selecting based on this so I can't do a "top down" query.

Update

I've obviously explained myself really badly here, so I'll try and clarify:

<ul class="x">
  <li>1</li>
  <li>2</li>
  <li>3</li>
</ul>
<ul class="y">
  <li>4</li>
  <li>5</li>
  <li>6</li>
</ul>

I have a jQuery object that already consists of elements 2,3,4 and 5. I want to select those elements who have a parent with the class = x.

Hope that makes more sense.

Answer 1

For a clean re-usable solution, consider extending the jQuery.fn object with a custom method used for determining the presence of a particular ancestor for any given element:

// Extend jQuery.fn with our new method
jQuery.extend( jQuery.fn, {
    // Name of our method & one argument (the parent selector)
    within: function( pSelector ) {
        // Returns a subset of items using jQuery.filter
        return this.filter(function(){
            // Return truthy/falsey based on presence in parent
            return $(this).closest( pSelector ).length;
        });
    }
});

This results in a new method, $.fn.within, that we can use to filter our results:

$("li").within(".x").css("background", "red");

This selects all list items on the document, and then filters to only those that have .x as an ancestor. Because this uses jQuery internally, you could pass in a more complicated selector:

$("li").within(".x, .y").css("background", "red");

This will filter the collection to items that descend from either .x or .y, or both.

Fiddle: http://jsfiddle.net/jonathansampson/6GMN5/