Keep the aspect ratio of your images using GIFs

create-gif.js

function createGif(width, height) {
  const buffer = new ArrayBuffer(24)
  const byteView = new Uint8Array(buffer)
  
  // signature
  byteView.set([ 71, 73, 70, 56, 57, 97 ], 0)
  
  // size
  byteView.set([width, width >> 8], 6)
  byteView.set([height, height >> 8], 8)
  
  // jibber jabber
  byteView.set([44], 13)
  byteView.set([1], 18)
  byteView.set([1], 20)
  byteView.set([2], 23)
  
  return btoa(String.fromCharCode.apply(null, byteView))
}