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>

The default scan reports only exact copies, and those are the ones to refactor first: an exact clone is almost always a real copy-paste. Two more passes find copies that were edited after pasting. They are noisier: they ignore names, values or a few statements on purpose, so they also surface blocks that merely look alike (models and DTOs, config tables, test setup, generated code, shared idioms). Run them only after the exact clones are dealt with, one family at a time, with tight settings, and treat what they report as leads to read rather than defects to fix:

# Type-2: renamed copies (other variable names, other constants), reported as "(renamed)".
# Raise --min-tokens: with identifiers ignored, a short block is mostly placeholders.
npx jscpd --reporters ai --ignore-identifiers --min-tokens 70 <path>

# Type-3: near-miss copies (one or two edited lines, or JS/TS/Python functions with the same structure),
# reported as "[~0.91 gap]" and "[~0.85 ast]". Widen only if the tight run finds nothing.
npx jscpd --reporters ai --max-gap-lines 1 --similarity <path>

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

Workflow