Note that the upstream node-opencv is not officially compatible with OpenCV 3+.
Stable tag :2.4.x is available.
Official Node.js "latest" image + OpenCV 3.4.0 (built from source, not a full stack) for npm install opencv to work.
onbuild tag is available.
(simpler way is to apt-get install libopencv-dev inside a node-based image)