Quick reference code for uploading an image to the Sanity Studio from the browser

upload-image-to-sanity.js

const getImageData = async url => {
  const response = await global.fetch(url)
  const contentType = response.headers.get("Content-Type")
  return response.blob().then(imageData => ({ contentType, imageData }))
}

const uploadImage = ({ imageData, contentType }) =>
  client.assets.upload("image", imageData, { contentType })

// usage example
const imageData = await getImageData(someUrl)
const image = await uploadImage(imageData)
console.log(image._id)