dry-refactoring

Guided workflow to eliminate copy-paste duplication in source code. Use after running jscpd to detect clones.

Prerequisites

First, run jscpd to identify duplications:

npx jscpd --reporters ai <path>

In codebases that mix related formats (e.g. JavaScript and TypeScript), add --cross-formats so clones spanning both are detected too:

npx jscpd --reporters ai --cross-formats "js-ts" <path>

On larger codebases, add --summary to get a refactoring-hotspot overview alongside the clone list — top files and folders with a dup% column showing how much of each file is duplicated:

npx jscpd --reporters ai --summary <path>

See the jscpd skill for full option reference, including cross-format group syntax and how to read the summary.

Workflow

1. Run jscpd with --reporters ai on the target path (add --summary on larger codebases to pick a starting point: files with high dup% and high token counts pay off most)
2. Parse each clone line to identify the two duplicated locations (file + line range)
3. Read both code fragments from the source files
4. Understand what the duplicated code does
5. Design a refactoring: extract a shared function, class, module, or constant
6. Apply the refactoring — update both locations and all other usages
7. Re-run jscpd to confirm the clone is eliminated
8. Repeat for remaining clones, highest-impact first

Refactoring Strategies

Extract function — when the duplicate is a block of logic:

// Before: same block in two places
// After: shared function called from both places

Extract module/utility — when the duplicate spans multiple files in different domains:

// Move shared logic to a shared utility file and import it

Extract constant or config — when the duplicate is repeated data or configuration.

Template/base class — when the duplicate is structural (e.g., repeated class shape).

Always ensure:

• All call sites are updated, not just the two reported by jscpd
• Tests still pass after refactoring
• The extracted abstraction has a clear, descriptive name

Tips

• Start with clones that have the highest line count — they have the most impact
• A clone between test files may indicate a missing test helper
• Clones across unrelated modules may signal a missing shared utility
• A cross-format clone (same logic in a .js and a .ts file, found with --cross-formats) often means code was ported without deleting the original — consolidate into one implementation (usually the TypeScript one) and update imports, rather than extracting a third shared copy
• Use --min-lines 10 to filter noise and focus on meaningful duplications