Why Repetition Is a Code Smell
When you start seeing the same few lines of code pop up again and again in your files, that’s usually a red flag. Repetition isn’t just about wasting space, it leads to bugs when you change something in one spot but forget to update the others. It also clutters your codebase, making things harder to read and harder to fix. Refactoring this repeated logic into functions not only shrinks your code but also makes it more reliable and easier to tweak down the line.

Spotting Patterns That Repeat Themselves
Finding repetition isn't always as simple as copy-paste detection. Sometimes the logic is the same, but the variable names or data types are different. You might see similar `if` conditions, loops, or formatting routines scattered around. Look for patterns in how data is handled, how results are calculated, or how output is structured. Once you start paying attention, you’ll notice these copycats everywhere—they're often hiding in plain sight.

Figure Out What the Repetition Is Actually Doing
Before you jump into refactoring, take a second to ask yourself what the repeated code is trying to accomplish. Is it formatting a date? Filtering data? Logging errors? Understanding the goal of the code helps you group it properly and avoid wrapping unrelated tasks together. Don’t just cut and paste into a function—look for the common purpose or outcome behind the similar logic. That’s what makes a function meaningful, not just shorter.

Turn Common Logic into a Function with a Name
Once you know what the repeated code is doing, bundle it into a function with a clear name that explains its job. The name acts like a mini comment, making the rest of your code easier to scan. Whether you're using Python, JavaScript, or anything else, the idea is the same: keep the function small, focused, and clear. That way, anyone reading the code later knows what’s going on without needing to dig through every line.

Add Parameters to Make the Function Reusable
Hardcoding values inside your function limits its usefulness. Instead, turn those values into parameters so you can pass in whatever you need each time. For example, if your original logic was printing user names with different formats, you could make the format a parameter. You can even set default values if some parameters are optional. This makes your function flexible without being complicated, and it helps keep duplication out of other parts of your code.

Step-by-Step Refactoring in Practice
The easiest way to refactor is to go slow. Start by finding one chunk of code you’ve repeated. Copy it into a function, replace the originals with calls to that function, and pass in any needed values. Then test to make sure it behaves the same way. You don’t need to refactor everything at once—start with low-hanging fruit and work your way up. Over time, your codebase will get leaner and easier to manage.

Make Sure Your New Function Works
After refactoring, don’t just assume everything works—test it. Run the program using the same inputs it handled before and check that the output is identical. If you have tests, update or expand them to cover the new function. Watch out for edge cases too, like empty values or weird input types. The goal is to be confident that your new function didn’t break anything and actually improved the code.

Refactor Smarter: Tips and Common Mistakes
Keep function names short but descriptive—they should tell you what the function does without needing a comment. Avoid turning every three-line repeat into a function just for the sake of it—group logic that truly belongs together. Don’t overgeneralize either, or you’ll end up with vague, hard-to-read code. Try not to let functions do too many things at once, and avoid unexpected side effects. And finally, always document the intent of a function so the next person (or future you) knows what it’s for at a glance.

Theophilus Edet

Function Definition and Invocation: Parameters, Return Types, and Scope of Function Syntax and Behaviour in 22 Languages[232843280



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