jQuery isChildOf - is element a child of / ancestor of element - plugin

If anyone knows of an existing jQuery method of determining whether an element is a child of another element, please feel free to post. I couldn't find one, so I developed the plugin below:

(function($) {
    $.fn.extend({
        isChildOf: function( filter_string ) {
          
          var parents = $(this).parents().get();
         
          for ( j = 0; j < parents.length; j++ ) {
           if ( $(parents[j]).is(filter_string) ) {
      return true;
           }
          }
          
          return false;
        }
    });
})(jQuery); 

The usage is:

$(element).isChildOf(filter_string)

where filter_string is any of the expr values that can be passed to JQuery's is() function. You can get more information here

example:

<div id="parent2">
  <div id="parent1">
    <div id="child">
    </div>
  </div>
</div>

Alerts "true":

alert( $('#child').isChildOf('#parent1') );

Alerts "true":

alert( $('#child').isChildOf('#parent2') );

Alerts "false"

alert( $('#child').isChildOf('#notaparent') );