http://benalman.com/code/javascript/jquery/jquery.ba-iff.js
/*!
 * iff - v0.2 - 6/3/2009
 * http://benalman.com/projects/jquery-iff-plugin/
 * 
 * Copyright (c) 2009 "Cowboy" Ben Alman
 * Licensed under the MIT license
 * http://benalman.com/about/license/
 */

(function($){
  '$:nomunge'; // Used by YUI compressor.

  $.fn.iff = function( test ) {
    var elems = !test || $.isFunction( test )
      && !test.apply( this, Array.prototype.slice.call(arguments, 1) )
      ? []
      : this;
    return this.pushStack( elems, 'iff', test );
  };

})(jQuery);

//---- yui

/*
 * iff - v0.2 - 6/3/2009
 * http://benalman.com/projects/jquery-iff-plugin/
 * 
 * Copyright (c) 2009 "Cowboy" Ben Alman
 * Licensed under the MIT license
 * http://benalman.com/about/license/
 */
(function($){$.fn.iff=function(b){var a=!b||$.isFunction(b)&&!b.apply(this,Array.prototype.slice.call(arguments,1))?[]:this;return this.pushStack(a,"iff",b)}})(jQuery);