index.js

var SlideList1 = ['img/wiggins_family.jpg', 'img/wiggins_dam2.jpg', 'img/wiggins_graduate.jpg', 'img/wiggins_labbench.jpg', 'img/wiggins_pibbles.jpg'];
var SlideShow1 = new SlideShow(SlideList1, 'slide1', 5000, "SlideShow1");

var SlideList2 = ['img/leone_loki.jpg', 'img/leone_xmas.jpg', 'img/leone_potter.jpg'];
var SlideShow2 = new SlideShow(SlideList2, 'slide2', 5000, "SlideShow2");

var SlideList3 = ['img/spresser_pupper1.jpg', 'img/spresser_pupper2.jpg', 'img/spresser_field.jpg'];
var SlideShow3 = new SlideShow(SlideList3, 'slide3', 5000, "SlideShow3");

function SlideShow(slideList, image, speed, name) {
  this.slideList = slideList;
  this.image = image;
  this.speed = speed;
  this.name = name;
  this.current = 0;
  this.timer = 0;
}

function switchImage(imgName, imgSrc) {
  if (document.images) {
    document.images[imgName].src = imgSrc;
  }
}

SlideShow.prototype.play = function () {
  with (this) {
    if (current++ == slideList.length - 1) current = 0;
    switchImage(image, slideList[current]);
    clearTimeout(timer);
    timer = setTimeout(name + '.play()', speed);
  }
};

window.onload = function () {
  SlideShow1.play();
  SlideShow2.play();
  SlideShow3.play();
};