Refactor Clean

Refactor & Clean Code

When to Use

• Code is correct but hard to read, modify, or extend
• Duplicated logic exists across multiple files
• Functions or classes have grown too large
• Preparing code for a new feature that requires structural changes
• After a rapid prototype that needs production-quality cleanup

Prerequisites

• Existing tests that cover the code to refactor (add tests first if missing)
• All tests passing before starting
• Code committed so you can revert if needed

Workflow

1. Identify Code Smells

# Find long files (likely doing too much)
Get-ChildItem -Recurse -Include *.ts,*.js,*.py,*.go | Where-Object { (Get-Content $_.FullName | Measure-Object -Line).Lines -gt 300 } | Select-Object FullName, @{N='Lines';E={(Get-Content $_.FullName | Measure-Object -Line).Lines}}

# Find duplicated string patterns
grep -rn "pattern-you-suspect-is-duplicated" src/ --include="*.ts"

# Find functions with too many parameters (>4 is a smell)
grep -n "function.*,.*,.*,.*," src/**/*.ts

Common smells to look for:

• Long functions (>40 lines) — extract smaller functions
• Duplicate code — extract shared utility
• Deep nesting (>3 levels) — use early returns or extract
• God objects — split into focused classes/modules
• Primitive obsession — introduce domain types
• Feature envy — move logic to the class that owns the data

2. Establish a Safety Net

# Run existing tests and record baseline
npm test 2>&1 | Tee-Object -Variable baseline
echo $baseline | Select-Object -Last 5

# If coverage is low, write characterization tests first
npm test -- --coverage --collectCoverageFrom="src/module-to-refactor.ts"

3. Plan the Refactoring

Before touching code, decide on the transformation:

• Extract Function — pull a block into a named function
• Extract Module — move related functions to a new file
• Rename — improve names for clarity
• Inline — remove unnecessary indirection
• Replace Conditional with Polymorphism — use strategy pattern
• Introduce Parameter Object — group related parameters

4. Make Small, Incremental Changes

Each change should be:

1. A single refactoring operation
2. Followed by running tests
3. Committed if tests pass

# After each refactoring step
npm test 2>&1 | Select-Object -Last 10

# If tests break, revert and try a smaller step
git checkout -- src/module-to-refactor.ts

5. Verify Behavior is Preserved

# Full test suite must still pass
npm test

# Compare coverage — it should not decrease
npm test -- --coverage

Examples

Extract Repeated Logic

// BEFORE: duplicated validation in multiple handlers
function createUser(data) {
  if (!data.email || !data.email.includes('@')) throw new Error('Invalid email');
  // ... create logic
}
function updateUser(data) {
  if (!data.email || !data.email.includes('@')) throw new Error('Invalid email');
  // ... update logic
}

// AFTER: extracted to a shared validator
function validateEmail(email: string): void {
  if (!email || !email.includes('@')) throw new Error('Invalid email');
}
function createUser(data) { validateEmail(data.email); /* ... */ }
function updateUser(data) { validateEmail(data.email); /* ... */ }

Flatten Deep Nesting with Early Returns

// BEFORE
function process(input) {
  if (input) {
    if (input.isValid) {
      if (input.data.length > 0) {
        return transform(input.data);
      }
    }
  }
  return null;
}

// AFTER
function process(input) {
  if (!input || !input.isValid || input.data.length === 0) return null;
  return transform(input.data);
}

Common Rationalizations

Red Flags

• Refactoring commit contains feature changes
• Dead code removed without any tests
• Type errors suppressed with // @ts-ignore or any types
• No verification that the same tests pass before and after refactoring
• Complex code left with "clean up later" TODO and no action

Verification

• npm test passes identically before and after the refactor
• Removed code confirmed as unused (grep -rn or IDE reference search)
• Complexity metrics improved (reduced function length, nesting depth)
• Refactor commit contains no feature changes (commit message: refactor:)
• PR describes the motivation for the refactor (why this code was cleaned up)

Tips

• Never refactor and add features in the same commit — keep them separate
• Use explore agent to understand call graphs before renaming or moving functions
• Use grep to find all callers before changing a function signature
• If tests are missing, write them first — refactoring without tests is gambling
• Commit after every successful small refactoring — you can always squash later
• The best refactoring is deleting code: look for dead code with grep and remove it