Simple js slideshow

slide.js

(function(){
  var index = 0,
      changeTime = 15000,
      slides = $(".slide");

  var select,
      nextSlide,
      previousSlide,
      interval;

  select = function(index){
      slides.each(function(idx,ele){
          $(ele).removeClass("active");
          if(idx === index){
            $(ele).addClass("active");
          }
      });
  };

  nextSlide = function(){
      index = (index>0)?index-1:slides.length-1;
      select(index);
  };

  previousSlide = function(){
      index = (index<slides.length-1)?index+1:0;
      select(index);
  };

  $(".left-arrow").on('click', function(){
    if(interval){
      clearInterval(interval);
      interval = setInterval(function(){nextSlide()},changeTime);
    }
    previousSlide();
  });

  $(".right-arrow").on('click', function(){
    if(interval){
      clearInterval(interval);
      interval = setInterval(function(){nextSlide()},changeTime);
    }
    nextSlide();
  });

  interval = setInterval(function(){nextSlide()},changeTime);
})();