So, I'm curious whether or not it would be possible to write scripts for a Unity game without using Unity itself, but using a third-party IDE, such as Visual Studio. My reason for this would be the following: I have a very low-end laptop, so I can not run Unity in any usable fashion. So I'm wondering if I could do the programming only part for the game without using Unity? By this, I mean writing the actual code and sending it over some online platform to be integrated with the Unity environment. And I know, this would not be productive at all.
So if I got your question correct, you don't want to open Unity but write the scripts that would work on it?
You CAN but you might not be sure about what you've written since it can not be tested without opening Unity. You might even solve syntax errors using intellisense (Visual Studio have intellisense for these) but if there's any logical error, calculation mistakes that you might've made, you will have to open up Unity to debug.
Since scripts are simple text files, you can write it on any IDE you want to, but testing will definitely require opening Unity.