var Throbber = new Class({
 initialize : function (target) {
  this.target  = $(target);
  this.status  = 0;
  this.img     = document.createElement('img');
  this.img.src = arguments[1] || './images/throbber.gif';
 },

 on : function() {
  if (this.status == 0) {
   this.target.appendChild(this.img);
   this.status = 1;
  }
 },

 off : function() {
  if (this.status == 1) {
   try { $(this.img).remove(); } catch(x) { }
   this.status = 0;
  }
 },

 toggle : function() {
  if (this.status)
   this.off();
  else
   this.on();
 }
});