Change image extension

Change image extension

Hi,

How do you replace an extension of an image on page load? I need to change the gif to png. 

  1.          var domainName = "http://www.domain.com/";
         if ((window.location.protocol + "//" + window.location.hostname + "/") == (domainName)) 
         
         {
         //what to do here?
         }

Thanks!