slider with autoplay function,using plain javascript.

slider-autoplay.js

var slideIndex = 1;
var t;
shwoSlides(slideIndex);

function pulsSlides(n)  {
  shwoSlides(slideIndex +=n);
}

function currentSlide(n) {
  shwoSlides(slideIndex = n);
}

function shwoSlides(n) {
  var i;
  var slides = document.getElementsByClassName("mySlides");
  var dots = document.getElementsByClassName("dot");
  if(n>slides.length){
    slideIndex = 1;
  }

  if(n<1){
    slideIndex = slides.length;
  }

  for(i=0;i<slides.length;i++){
    slides[i].style.display = "none";
  }

  for(i = 0;i<dots.length;i++){
    dots[i].className=dots[i].className.replace('active','');
  }

  slides[slideIndex-1].style.display = "block";
  dots[slideIndex-1].className+=" active";

}

function autoPlay() {
   var i;
    var slides = document.getElementsByClassName("mySlides");
    for (i = 0; i < slides.length; i++) {
        slides[i].style.display = "none";
    }
    slideIndex++;
    if (slideIndex> slides.length) {slideIndex = 1}
    slides[slideIndex-1].style.display = "block";
    t=setTimeout('autoPlay()', 2000); // Change image every 2 seconds
}