copy EXIF from one JPEG blob to another and return a new JPEG blob.

copyExif.js

// Copyright (c) 2019 Jian Weihang <tonytonyjan@gmail.com>

export default async (src, dest) => {
  const exif = await retrieveExif(src);
  return new Blob([dest.slice(0, 2), exif, dest.slice(2)], {
    type: "image/jpeg"
  });
};

export const SOS = 0xffda,
  APP1 = 0xffe1,
  EXIF = 0x45786966,
  retrieveExif = blob =>
    new Promise((resolve, reject) => {
      const reader = new FileReader();
      reader.addEventListener("load", ({ target: { result: buffer } }) => {
        const view = new DataView(buffer);
        let offset = 0;
        if (view.getUint16(offset) !== 0xffd8)
          return reject("not a valid jpeg");
        offset += 2;

        while (true) {
          const marker = view.getUint16(offset);
          if (marker === SOS) break;
          const size = view.getUint16(offset + 2);
          if (marker === APP1 && view.getUint32(offset + 4) === EXIF)
            return resolve(blob.slice(offset, offset + 2 + size));
          offset += 2 + size;
        }
        return resolve(new Blob());
      });
      reader.readAsArrayBuffer(blob);
    });