Jquery methods?

I keep seeing codes like this:

  $(document.documentElement).keyup( function(event) {
    var slides = $('#slides .pagination li'),
        current = slides.filter('.current');

    switch( event.keyCode ) {
      case 37: // Left arrow
        if ( slides.filter(':first').is( current ) ) {
          slides.filter(':last').find('a').click();
       开发者_开发技巧 } else {
          slides.eq( slides.index(current) - 1 ).find('a').click();
        }
        break;
      case 39: // Right arrow
        if ( slides.filter(':last').is( current ) ) {
          slides.filter(':first').find('a').click();
        } else {
          current.find('+ li').filter(':first').find('a').click();
        }
        break;
    }
  });

For a line like this: current = slides.filter('.current');, .filter() is a jquery method, right? Then shouldn't it be current = $(slides).filter('.current');.

Does it work the way it is done in the code? Why?

slides is a jQuery object so you don't need to wrap it in $() like you do with a DOM object.

So slides.filter('.current') works like $('#slides .pagination li').filter('.current'). It's important to keep track of whether your objects are jQuery selectors, jQuery objects, and/or DOM objects.

Some people like to name their jQuery objects like var $slides as a mental note.

slides is already 'jQuery'ed: notice that it's defined using the $ sign. so there's no need to wrap it with a $ again.