I know python fairly well, and had previously done most web development with flask or django. I had to learn JS so that I could do front end web dev, things like D3 and such for visualizations of data. I tried out a few of the frameworks that I came across for back-end web dev as well, things like Koa, knex, passport, etc - and I have to say that these days I start far more projects as JS/Node.JS projects than I do python.

I still love and use python quite often, but more in data analysis/manipulation projects with Jupyter - Node definitely doesn't have anything on python in that dept.

p.s., check out pandas if you're not already familiar with it.