preload = new Array();
preload['default'] = new Image;
preload['default'].src = 'products/default-show.jpg';

function loadImage(des) {
  preload[des] = new Image;
  preload[des].src = 'products/'+des+'-show.jpg';
}
function showImage(des) {
  show = document.getElementById('showcase');
  show.src = preload[des].src;
}