Test for webp image support. From: http://stackoverflow.com/questions/5573096/detecting-webp-support#10930441

testWebpSupport.js

function testWebP(callback) {
  var webP = new Image();
  webP.src = 'data:image/webp;base64,UklGRjoAAABXRUJQVlA4IC4AAACyAgCdASoCAAIALmk0mk0iIiIiIgBoSygABc6WWgAA/veff/0PP8bA//LwYAAA';
  webP.onload = webP.onerror = function () {
    callback(webP.height === 2);
  };
};

function notify(supported) {
  console.log((supported) ? "webP supported!" : "webP not supported.");
}

testWebP(notify);​