Create thumbnail with GM and NodeJS

gm('image.jpg')
  .size((err, size) => {
    if (!err) {
      if (size.width > size.height)
        gm(image).thumb(160, 120, 'image_thumb.jpg', 100, (err) => console.log(err))
      else if (size.width < size.height)
        gm(image).thumb(120, 160, 'image_thumb.jpg', 100, (err) => console.log(err))
    }
})