Looking for dead code

The N26 web platform has about 1,000 components and over 300 helpers. It’s not a huge code base per se (certainly not Facebook size anyway), but with over 250,000 lines of code, it is definitely on the big side of the spectrum.

In an ever-growing code base, it can be tedious, not to mention difficult, to look for code that is no longer used (or “dead code”). It cannot realistically done by hand, and I don’t know any solid tool that can automate that entirely.

So I wrote a small Bash script to take its best guess as to which files were no longer used. To detect that, I rely on the fact that all our imports look the same. For instance:

import Input from "@components/Input";
import looksLikeEmail from "@helpers/looksLikeEmail";

This means if we search for /Input' and find no result, it means the Input component is never imported anywhere. This only works because we never add /index or /index.js at the end of our imports.

Now, we only have to loop through all paths in our components directory (or any other), and perform a search for every one of them. If the search yields nothing, the component is unused.

# Loop over every entry within the given path
for entry in src/components/*
do
  # Grab only the directory name
  # (e.g. `Input` from `src/components/Input`)
  name=$(basename $entry)

  # Perform a search in the `./src` directory
  # and echo the path if it yields nothing
  if [[ -z "$(grep -r "/$name'" ./src)" ]]; then
    echo "$entry is unused"
  fi
done

A convenient way to execute that code is to define it as a function in one’s .bashrc or .zshrc file. When wrapped as a function, it might look like this:

function groom {
  root="${2:-.}"
  for entry in "$1"/*
  do
    name=$(basename $entry)
    if [[ -z "$(grep -r "/$name'" $root)" ]]; then
      echo "$entry is unused"
    fi
  done
}

It can then be used by passing the folder to ‘groom’ as an argument, and the root directory for the code search as a second argument (./ by default):

groom src/components
groom src/components src

It’s not much, but I hope this helps you finding some dead code without having to rely on build tools or dependencies. It’s a pretty low hanging fruit. ✨