Before you think about selling code online, here's a couple questions to see if you're ready:
How would you feel if you found people stealing/sharing/pirating your code for free?
How would you feel if you found 5 people reselling your code as their own code, maybe even making more money than you?
When was the last time you bought a font? When I was in college I interviewed a type designer and spoke to a few others and they were all the most bitter group of people you could imagine. They were sick and tired of people always stealing their stuff and felt entitled to money they never earned etc etc. I had been considering moving into that field but I didn't want to turn into a bitter old man.
Later I've seen websites like Envato network where you can post code and people can buy it, and I'm sure they try their best to stop people reselling works they don't have a right to, but I'm sure it still happens, and you may never be able to track down who it is and get them to stop.
If this would bother you, maybe selling such an easy-to-copy and hard-to-enforce thing isn't the right move.
For me, the right move was to release all my code for free, open-source, and have people hire me to either write new code that doesn't exist yet, or to write the code that they need specifically. That way it doesn't really matter who has the code after it exists, or how many times it's copied, I get paid 1x to write it 1x and then it's out there.