Java script or rails?

Hey everyone. Aspiring developer here. I want to get into the tech space and build products of my own. I’m currently co-founding my own startup and I’ve built an MVP on bubble. I really want to expand my skills but I’m facing it hard as there are little to no tutorials on building Shopify apps(my main interest)

Is there anyone out there having experience that could shed light on my predicament?

Thank you in advance