Jscpd

Common Options

Workflow

1. Run jscpd with --reporters ai on the target path
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
• Use --min-lines 10 to filter noise and focus on meaningful duplications