function ajax_delete_url(url, params, callback){
    $.ajax({ url: url, type: 'DELETE', data: params, success: callback });
  }

  function ajax_get_url(url, params, callback){
    $.ajax({ url: url, type: 'GET', data: params, success: callback });
  }

  function ajax_post_url(url, params, callback){
    $.ajax({ url: url, type: 'POST', data: params, success: callback });
  }