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

    this.setProps = function(oProps){
      for(varName in oProps){
        this[varName] = oProps[varName];
      }

      propSet = true;
    }

    this.readProp = function(prop){
      return this[prop];
    }

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


      var a = new animation();
      a.setProps({
        'start' : -21,
        'end'   : 0,
        'time'  : 3,
        'style' : 'top'
      });
      console.log(a.readProp('propSet'));