Before learning React (which is a JavaScript Library), you're going to want to learn drumroll JavaScript! After you become comfortable with JS, then you can move onto learning React as it will build upon your existing knowledge. This will enable you to build the front-end (user interface) of applications.

Following that, you'll want to learn Node.js, a run-time environment, for back-end, server-side development. This enables Unix network programming using JavaScript-based syntax.

(Optional) Learn TypeScript for the sake of static typing, which will enable you to catch errors in your code much sooner than you would otherwise. Here's a good link: https://medium.com/swlh/the-major-benefits-of-using-typescript-aa8553f5e2ed

Python is great for automating back-end processes within an organization as well as for data science when applied with Jupyter Notebooks.

I hope this helps!