//constructor
function Animation(){
    this.interval = false,
    propSet = false,
    this.start = 0,
    this.end = 0,
    this.time = 0,
    this.style = '';

      propSet = true;
    }

    console.log(start);

    if(!this.interval) this.interval = setInterval(function(){}, 50);
  };

  Animation.prototype.setProps = function(oProps){
      for(varName in oProps){
        if( oProps.hasOwnProperty("" + varName){
      this["" + varName] = oProps[varName];
    }
      }


//instantiation
      var a = new Animation();
      a.setProps({
        'start' : -21,
        'end'   : 0,
        'time'  : 3,
        'style' : 'top'
      });