index.js

import GIF from 'omggif';
import { GifUtil, GifFrame, BitmapImage, GifCodec } from 'gifwrap';

const MIME_TYPE = 'image/gif';

export default () => ({
  mime: { [MIME_TYPE]: ['gif'] },

  constants: {
    MIME_GIF: MIME_TYPE
  },

  decoders: {
    [MIME_TYPE]: data => {
      const gifObj = new GIF.GifReader(data);
      const gifData = Buffer.alloc(gifObj.width * gifObj.height * 4);

      gifObj.decodeAndBlitFrameRGBA(0, gifData);

      return {
        data: gifData,
        width: gifObj.width,
        height: gifObj.height
      };
    }
  },

  encoders: {
    [MIME_TYPE]: data => {
      const bitmap = new BitmapImage(data.bitmap);
      GifUtil.quantizeDekker(bitmap, 256);
      const newFrame = new GifFrame(bitmap);
      const gifCodec = new GifCodec();
      return gifCodec.encodeGif([newFrame], {}).then(newGif => {
        return newGif.buffer;
      });
    }
  }
});