Find the size of a gif by requesting only 4 bytes

gifsize.js

await gifsize('https://media.giphy.com/media/3ornjZLITGcFQVRbxK/source.gif')
// > {width: 500, height: 247}


async function gifsize (url) {
    const result = await fetch(url, {headers: {Range: 'bytes=6-9'}})

    const [width, height] = new Uint16Array(await result.arrayBuffer())

    return {width, height}
}