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quality.","url":"https://app.codemod.com/registry/javascript-prefer-set-size-over-length","publisher":{"@id":"https://app.codemod.com#org"},"image":"https://avatars.githubusercontent.com/u/6104558?v=4","isAccessibleForFree":true,"license":"MIT","version":"0.1.0","keywords":["javascript","typescript","set","code-quality"],"datePublished":"2026-05-05 23:01:20.395471+00","dateModified":"2026-05-05 23:01:20.395471+00"},{"@type":"SoftwareApplication","@id":"https://app.codemod.com/registry/javascript-prefer-set-size-over-length#app","name":"javascript-prefer-set-size-over-length codemod","description":"Replace incorrect or non-idiomatic `set.length` reads with `set.size` for variables/expressions statically known to be `Set` instances in JavaScript/TypeScript codebases, improving correctness and code quality.","url":"https://app.codemod.com/registry/javascript-prefer-set-size-over-length","publisher":{"@id":"https://app.codemod.com#org"},"softwareVersion":"0.1.0","applicationCategory":"DeveloperApplication","operatingSystem":"Cross-platform","offers":{"@type":"Offer","price":"0","priceCurrency":"USD","availability":"https://schema.org/InStock"}}]}4a:T6a9,# javascript-prefer-set-size-over-length Replace incorrect `Set` cardinality reads like `set.length` with `set.size` when the receiver is statically proven to be a built-in `Set` or `ReadonlySet`. ## What It Rewrites - `const s = new Set(values); s.length` -> `s.size` - `function f(s: Set) { return s.length; }` -> `return s.size` - `maybeSet?.length` -> `maybeSet?.size` when the type is `Set | nullish` - `set['length']` -> `set.size` by default, or `set['size']` with `--param computed_style=computed` - Reads narrowed by `instanceof Set`, `Object.prototype.toString.call(x) === '[object Set]'`, or a user-defined type guard returning `x is Set<...>` - Safe `const` aliases such as `const alias = set` - `this.cache.length` and typed property reads when the property is declared as `Set<...>` or `ReadonlySet<...>` ## Safety Rules - Skips unknown or ambiguous receivers - Skips arrays, strings, functions, typed arrays, and other normal `.length` reads - Skips write/update/delete contexts such as `set.length = 1`, `set.length++`, and `delete set.length` - Skips dynamic keys like `set[key]` - Skips visible subclass overrides such as `new CustomSet().length` - Excludes `node_modules`, `dist`, `build`, `coverage`, and `vendor` paths by default ## Usage ```bash # Run the published codemod npx codemod javascript-prefer-set-size-over-length -t /path/to/repo # Run the local package pnpm dlx codemod@latest workflow run -w . -t /path/to/repo # Preserve computed access for string-literal keys pnpm dlx codemod@latest workflow run -w . -t /path/to/repo --param computed_style=computed ``` ## Development ```bash pnpm test pnpm run 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