Every time I start a new project, I organize the code I’m looking at into three types, or categories if you like. And I think these types can be applied to any codebase, any language, any technology or open source project. Whether I’m writing HTML or CSS or building a React component, thinking about these different categories has helped me figure out what to refactor and prioritize, and what to leave alone for now.

Those categories: Boring Code, Salt Mine Code, and Radioactive Code.

Let me explain.

Boring Code

Boring code is when it makes perfect sense when you read it. There’s no need to refactor it, and it performs its function in a way that doesn’t make you want to throw yourself into a river. Boring code is good code. It doesn’t do a kick-flip and it’s not trying to impress you. You can use it without having to write even more code or engineer hacks on top of it. Boring code does exactly what it says on the tin and never causes any surprises.

This function makes sense, this prop is clearly named, this React component is straightforward. There are no loops within loops, no mental gymnastics required here.

However, boring code is near impossible to write because our understanding of it is almost always incomplete when we start tackling a problem. Just look at how many considerations can go into a styling a simple paragraph for contrast. To write boring code, we must be diligent, we must endlessly refactor, and we must care for the codebase beyond a paycheck at the end of the month.

Boring code is good because boring code is kind.

Salt Mine Code

This is the type of code that’s bonkers and makes not a lick of sense. It’s the sort of code that we can barely read but it’s buried so deep in the codebase that it’s near impossible to change anyway. However! It’s not leaking into other parts of our code, so we can mostly ignore it. It might not be pretty, and we probably don’t want to ever look at it so long as we live, but it’s not actively causing any damage.

It’s this type of code that we can mostly forget about. It’s the type of code that is dangerous if opened up and tampered with, but for now, everything is okay.

The trouble is buried deep.

Radioactive Code

Radioactive code is the real problem at the heart of every engineering team. It’s the let’s-not-go-to-work-today sort of code. It’s the stuff that is not only bad but is actively poisoning our codebase and making everything worse over time. Imagine a codebase as a nuclear reactor; radioactive code is the stuff that’s breached the container and is now leaking into every part of our codebase.

An example? For us at Gusto and on the design systems team, I would consider our form components to be radioactive. Each component causes more problems because we can never use the component as is; we have to hack it to get what we want. Each time anyone uses this code they have to write even more code on top of it, making things worse over time, and it encourages everyone on the team to do the same.

In our design system, when we want to add a class name to the div that wraps a form element, we must use the formFieldClass prop in one component, and wrapperClass in another. There is a propType called isDefaultLayout and everyone sets it to false and writes custom CSS classes on top of it. In other words, not only does radioactive code make it hard for us to understand all this nonsense code, it makes it increasingly difficult to understand other parts of the codebase, too. Because the file we’re looking at right now has dependencies on eight different things that we cannot see. The result of removing this radioactive code means changing everything else that depends upon it.

In other words, radioactive code — like our form components — makes it impossible for the codebase to be trusted.

Radioactive code is not only bad for us and our codebase, but it is also bad for our team. It encourages bad habits, cruelty in Slack threads, not to mention that it causes friction between team members that is hard to measure. Radioactive code also encourages other teams in a company to go rogue and introduce new technologies into a codebase when the problem of radioactive code is not the tech itself. Anyone can write this type of code, regardless of the language or the system or the linting when they’re not paying enough attention to the problem. Or when they’re trying to be a little too smart. Or when they’re trying to impress someone.

How do we fix radioactive code? Well, we must draw a circle around it and contain the madness that’s leaking into other parts of the codebase. Then we must do something utterly heroic: we must make it boring.