How common is it to use 3rd party libraries? I feel like I might be too reliant on them. What's a good balance of using them to expedite certain aspects of coding, and relying on them?

They are used all over the place. Never reinvent the wheel. There is no purpose. Picking up a third party library makes you develop faster (because you do not need to write your own) plus the libraries mainteneners have more time to spare into the library (because youll need the time for the application).if you would use your own one you would need to maintain two code bases.

You shouldn't pick libraries that are 5 years old and never have seen any git interaction whatsoever. But any library, especially the ones Google, airbnb, Facebook, Netflix, Microsoft) will be a safe bet I'd it has seen some activity the last year or two.

In an average web app, I probably have 20 or so prod dependencies, another 30 Dev dependencies; there are probably 200+ libs in my node_modules folder, of which maybe 1 or 2 I've written.

So yes, at least in the web sphere, it's very common.

If you are scared of being reliant on a 3rd party library, just write a wrapper. Worst case scenario, you have to rewrite the wrapper and the app will still work...

I'll code an extra 200 lines if it means I don't have to use a library… don't judge me.