questa è la versione funzionante e corretta della classe...se a qualcuno servisse per delle modifiche eccola...
Codice PHP:
    function Slider(cosa){
        
this.vel 1;
        
this.mov 1;
        
this.id cosa;
        
this.start 100-document.getElementById(this.id).offsetHeight;
        var 
scope this;
        
this.end this.start+document.getElementById(this.id).offsetHeight;
        
document.getElementById(this.id).style.top=this.start+"px";
            function 
getPosition(){
                return 
parseInt(document.getElementById(scope.id).style.top);
            };
            function 
scendilo(){
                    
document.getElementById(scope.id).style.top getPosition() + scope.mov "px";
                    if (
getPosition() >= scope.endclearInterval(timeout);
            };
            function 
salilo(){
                    
document.getElementById(scope.id).style.top getPosition() - scope.mov "px";
                    if (
getPosition() <= scope.startclearInterval(timeout);
            };
            
this.move = function(){
                if (
getPosition() == this.starttimeout setInterval(scendiloscope.vel);
                else 
timeout setInterval(saliloscope.vel);
            }
    }