ffmpeg extract video frames from url to a local variable in Node

Question

I'm using the Nodejs spawn() functionality to execute a shell command that goes like this:

ffmpeg -i https://someUrl.com/someVideo.mp4 -vf fps=30 frame-%d.bmp

Which works for me as to saving 30 frames per second into numbered files, but I'd like to save every frame into a local variable so I could parse it in whatever way I need to (specifically to a JSON).

What would be the best way to do so?

Thanks in advance.