<script type="text/javascript">
jQuery.cookie = function(name, value, options) {
  if (typeof value != 'undefined') {
  options = options || {};
  if (value === null) {
  value = '';
  options.expires = -1;
  }
  var expires = '';
  if (options.expires && (typeof options.expires == 'number' || options.expires.toUTCString)) {
  var date;
  if (typeof options.expires == 'number') {
  date = new Date();
  date.setTime(date.getTime() + (options.expires * 24 * 60 * 60 * 1000));
  } else {
  date = options.expires;
  }
  expires = '; expires=' + date.toUTCString();
  }
  var path = options.path ? '; path=' + (options.path) : '';
  var domain = options.domain ? '; domain=' + (options.domain) : '';
  var secure = options.secure ? '; secure' : '';
  document.cookie = [name, '=', encodeURIComponent(value), expires, path, domain, secure].join('');
  } else {
  var cookieValue = null;
  if (document.cookie && document.cookie != '') {
  var cookies = document.cookie.split(';');
  for (var i = 0; i < cookies.length; i++) {
  var cookie = jQuery.trim(cookies[i]);
  if (cookie.substring(0, name.length + 1) == (name + '=')) {
  cookieValue = decodeURIComponent(cookie.substring(name.length + 1));
  break;
  }
  }
  }
  return cookieValue;
  }
};</script>

$.cookie('cookie_name', 'cookie_text', {expires: 365, path: '/'});

$.cookie('cookie_name', null, {expires: 365, path: '/'});

$.cookie('cookie_name');

<script type="text/javascript">
$(document).ready(function(){
var cookie = $.cookie('show_alert');
if (cookie==null) {
$.cookie('show_alert', 'stop_show', {expires: 365, path: '/'});
alert('Ты видишь это первый и последний раз.');
}
});
</script>

<a href="javascript:;" onclick="$.cookie('show_alert', null, {expires: 365, path: '/'});">очистить</a>