This snippet checks if browser supports web

check_if_webp_supported.js

function supportsWebP () {
  const canvas = typeof document === 'object'
    ? document.createElement('canvas')
    : {}

  canvas.width = canvas.height = 1

  return canvas.toDataURL
    ? canvas.toDataURL('image/webp').indexOf('image/webp') === 5
    : false
}