// ****** THE CLASS
var Loop=new Class({loopCount:0,isStopped:true,isLooping:false,loopMethod:$empty,setLoop:function(fn,delay){if(this.isLooping)this.stopLoop();this.loopMethod=fn;this.loopDelay=delay||3000;return this;},stopLoop:function(){this.isStopped=true;this.isLooping=false;$clear(this.periodical);return this;},startLoop:function(delay){if(this.isStopped){var delay=(delay)?delay:this.loopDelay;this.isStopped=false;this.isLooping=true;this.periodical=this.looper.periodical(delay,this);}
return this;},resetLoop:function(){this.loopCount=0;return this;},looper:function(){this.loopCount++;this.loopMethod(this.loopCount);return this;}});

// ****** IMPLEMENTING CLASS EXAMPLE

var LoopTest = new Class({
  
  Implements: Loop,
  
  initialize: function(log){
    this.setLoop(this.update, 1000);
    this.log = document.id(log);
  },
  
  update: function(count){
    this.log.set('text',"Looped " + count + " times.");
  }
  
});


// ****** USAGE

loop = new LoopTest('log');

$('start').addEvent('click',function(){
  loop.startLoop();
});
  
$('stop').addEvent('click',function(){
  loop.stopLoop();
});
 
$('reset').addEvent('click',function(){
  loop.resetLoop();
});
  
$('change_delay').addEvent('click',function(){    
  loop.stopLoop()
  .resetLoop()
  .startLoop($('delay').value);
});

    <h1>Loop.js Demo/Test</h1>
    <h2 id="log">Waiting...</h2>
    <div id="actions">
        <h3>Public Methods</h3>
        <p>
            <button id="start">start</button> <button id="stop">stop</button> <button id="reset">reset</button>
        </p>
        <h3>State Tweaking</h3>
        <p>
            Delay: <input type="text" size="6" id="delay" value="1000" /> <button id="change_delay">Restart</button>
    </div>

MooShell