JavaScript snippet to replace all jpeg images with webp images to reduce network bandwidth.

jpeg-webp.js

window.onload = function() {
    var supportsWebP = Modernizr.webp;
    var allImages = document.body.getElementsByTagName("img");
    var length = allImages.length;
    for(i = 0; i < length; i++){
      var image = allImages[i];
      var imgSource = image.getAttribute('data-img-source');
      image.src = supportsWebP ? imgSource.replace('.jpg', '.webp') : imgSource;
    }
}