change an image when the mouse pointer hovers over it. change it back when the mouse pointer leaves the image. do it in vanilla javascript without html.

var img = document.createElement('img');
img.src = 'http://www.google.com/intl/en_ALL/images/logo.gif'
img.onmouseover = function(){
  this.src = 'http://blog.addthiscdn.com/wp-content/uploads/2015/11/logo-e1447343434143.png'
}
img.onmouseout = function(){
  this.src = 'http://www.google.com/intl/en_ALL/images/logo.gif'
}