How can I change the class of an element with jQuery>

I have a JavaScript function that looks like this:

function UpdateFilterView() {
  if (_extraFilterExists) {
    if ($('#F_ShowF').val() == 1) {
      $('#extraFilterDropDownButton').attr('class', "showhideExtra_up");
      $('#extraFilterDropDownButton').css("display", "block");
      if ($('#divCategoryFilter').css("display") == 'none') {
        $('#divCategoryFilter').show('slow');
      }
      return;
    } else {
      if ($('#divCategoryFilter').css("display") == 'block') {
        $('#divCategoryFilter').hide('slow');
      }

      $('#extraFilterDropDownButton').css("display", "block");
      $('#extraFilterDropDownButton').attr('class', "showhideExtra_down");
      return;
    }
  } else {
    if ($('#divCategoryFilter').css("display") != 'none') {
      $('#divCategoryFilter').hide('fast');
    }
    $('#extraFilterDropDownButton').css("display", "none");
  }
}

This will be triggered by the following code (from within the $(document).ready(function () {}):

$('#extraFilterDropDownButton').click(function() {
	if ($('#F_ShowF').val() == 1) {
		$('#F_ShowF').val(0);
	} else {
		$('#F_ShowF').val(1);
	}

	UpdateFilterView();
});

The HTML for this is easy:

<div id="divCategoryFilter">...</div> 
<div style="clear:both;"></div>
<div id="extraFilterDropDownButton" class="showhideExtra_down">&nbsp;</div>

I have two problems with this:

1. When the panel is hidden and we press the div button (extraFilterDropDownButton) the upper left part of the page will flicker and then the panel will be animated down.

2. When the panel is shown and we press the div button the panel will hide('slow'), but the button will not change to the correct class even when we set it in the UpdateFilterView script?

The correct class will be set on the button when hovering it, this is set with the following code:

$("#extraFilterDropDownButton").hover(function() {
    if ($('#divCategoryFilter').css("display") == 'block') {
      $(this).attr('class', 'showhideExtra_up_hover');
    } else {
      $(this).attr('class', 'showhideExtra_down_hover');
    }
  },
  function() {
    if ($('#divCategoryFilter').css("display") == 'block') {
      $(this).attr('class', 'showhideExtra_up');
    } else {
      $(this).attr('class', 'showhideExtra_down');
    }
  });

To set a class completely, instead of adding one or removing one, use this:

$(this).attr("class","newclass");

Advantage of this is that you'll remove any class that might be set in there and reset it to how you like. At least this worked for me in one situation.

Use jQuery's

$(this).addClass('showhideExtra_up_hover');

and

$(this).addClass('showhideExtra_down_hover');

<script>
$(document).ready(function(){
      $('button').attr('class','btn btn-primary');
}); </script>

I like to write a small plugin to make things cleaner:

$.fn.setClass = function(classes) {
    this.attr('class', classes);
    return this;
};

That way you can simply do

$('button').setClass('btn btn-primary');