get image size without downloading full image,

getSize.js

// Currently works for jpeg only,
// CROS should be enable 

// JPEG SPECS:
// http://vip.sugovica.hu/Sardi/kepnezo/JPEG%20File%20Layout%20and%20Format.htm
async function getSize(url) {

  const response = await fetch(url);
  const reader = response.body.getReader();
  const {value, done} = await reader.read();
  let width, height;
  for (let i = 0; i <= value.length; i++) {
    if (value[i] === 255 && value[i + 1] === 194) {
      height = (value[i + 5] * 255) + value[i + 6] + 2;
      width  = (value[i + 7] * 255) + value[i + 8] + 4;
      break;
    }
  }

  reader.cancel();
  return {width, height}
}


getSize('https://images.unsplash.com/photo-1504964148034-86ded740d1e2?dpr=1&auto=compress,format&fit=crop&w=2850&h=&q=80&cs=tinysrgb&crop=').then(r => console.log(r));