Function for detecting support of webp

canIUseWebp.js

// thank http://jsfiddle.net/Schepp/uZDHY/ for idea
const canIUseWebp = () => {
  return new Promise((resolve, reject) => {
  // create image
  const webp = new Image();
  // detect if browser can read format
  webp.onerror = () => reject('Your browser does not suppoert WebP');
  webp.onload = () => resolve('Your browser supports WebP, yay!');
  // just 1px blank webp image
  webp.src = 'data:image/webp;base64,UklGRiQAAABXRUJQVlA4IBgAAAAwAQCdASoBAAEAAsBMJaQAA3AA/veMAAA=';
  });
};

// how to use
// canIUseWebp().then(e => console.log(e)).catch(err => console.log(err))