/* if and else to shown image */
var image = document.createElement('img');
if (Math.random() > 0.5) {
  image.src = 'http://www.catgifpage.com/gifs/318.gif';
} else {
  image.src = 'http://www.catgifpage.com/gifs/320.gif';
}
document.body.appendChild(image);