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Chiribuc"},"license":"MIT","homepage":"https://github.com/chiribuc/damerau-levenshtein#readme","keywords":["damerau-levenshtein","levenshtein","edit-distance","string-distance","fuzzy-search","spell-check","typescript"],"repository":{"type":"git","url":"git+https://github.com/chiribuc/damerau-levenshtein.git"},"description":"Fast, dependency-free Damerau-Levenshtein edit distance with configurable operation costs.","maintainers":[{"name":"crobert","email":"me@crobert.dev"}],"readme":"# Damerau-Levenshtein\n\n[](https://www.npmjs.com/package/@crob/damerau-levenshtein)\n[](https://github.com/chiribuc/damerau-levenshtein/actions/workflows/ci.yml)\n[](./LICENSE)\n\nThe Damerau-Levenshtein edit distance: the cost of turning one string into another using\ninsertions, removals, substitutions, and transpositions of adjacent characters.\n\n- **Dependency-free** and tiny โ about 1.2 kB gzipped.\n- **TypeScript-first**, with types for every cost callback.\n- **Configurable costs** per operation, as flat numbers or per-character functions.\n- **Unicode-aware**: compares code points, so emoji count as one character.\n- **Linear memory**: O(min(n, m)), so long strings stay cheap.\n- Ships **ESM, CommonJS and UMD** builds.\n\n## Installation\n\n```sh\nnpm i @crob/damerau-levenshtein\n```\n\n## Usage\n\n```ts\nimport { DamerauLevenshtein } from \"@crob/damerau-levenshtein\";\n\nconst dl = new DamerauLevenshtein();\n\ndl.distance(\"kitten\", \"sitting\"); // 3\ndl.distance(\"ab\", \"ba\"); // 1 โ one transposition\n```\n\nComparing a single pair? Use the `distance` helper instead:\n\n```ts\nimport { distance } from \"@crob/damerau-levenshtein\";\n\ndistance(\"kitten\", \"sitting\"); // 3\ndistance(\"ab\", \"ba\", { transpositions: false }); // 2\n```\n\nThe class is also available as a default export, and the package works from CommonJS:\n\n```js\nconst { DamerauLevenshtein, distance } = require(\"@crob/damerau-levenshtein\");\n```\n\nIn the browser, the UMD build exposes everything on `window.DamerauLevenshtein`:\n\n```html\n\n\n```\n\n## API\n\n### `new DamerauLevenshtein(options?)`\n\nCreates a reusable calculator. Options are validated once, at construction, so build the\ninstance once and reuse it across comparisons.\n\n| Option | Type | Default | Description |\n| ---------------- | ----------------------------------------- | ------- | --------------------------------------------------------- |\n| `insert` | `number \\| (char) => number` | `1` | Cost of inserting a character from the target. |\n| `remove` | `number \\| (char) => number` | `1` | Cost of removing a character from the source. |\n| `substitute` | `number \\| (from, to) => number` | `1` | Cost of replacing one character with another. |\n| `transpose` | `number \\| (backward, forward) => number` | `1` | Cost of swapping two adjacent characters. |\n| `transpositions` | `boolean` | `true` | Set to `false` to compute the plain Levenshtein distance. |\n\nCosts must be finite and `>= 0`. Unknown options, out-of-range costs, and wrongly typed\nvalues throw rather than being silently ignored.\n\n### `dl.distance(source, target)`\n\nReturns the cost of transforming `source` into `target`. Throws a `TypeError` if either\nargument is not a string.\n\n### `distance(source, target, options?)`\n\nOne-shot convenience wrapper that constructs a `DamerauLevenshtein` and calls `distance`.\n\n### Types\n\n`DamerauLevenshteinOptions`, `CharCostFunction`, `SubstituteCostFunction`,\n`TransposeCostFunction`, and `Cost` are all exported.\n\n## Custom costs\n\nCosts can be flat numbers or functions of the characters involved โ useful when, say, a\ntypo on an adjacent keyboard key should count for less than an unrelated character:\n\n```ts\nconst dl = new DamerauLevenshtein({\n insert: 1,\n remove: 0.5,\n substitute: (from, to) => (from === \"a\" && to === \"e\" ? 0.3 : 1),\n transpose: (backward, forward) => (backward === \"n\" ? 0.5 : 1),\n});\n\ndl.distance(\"apple\", \"epple\"); // 0.3\n```\n\n`substitute` receives `(from, to)`: the source character and the target character it is\nreplaced with. `transpose` receives `(backward, forward)`: the two adjacent source\ncharacters being swapped, in the order they appear in `source`.\n\nTo compute the plain Levenshtein distance, turn transpositions off:\n\n```ts\nnew DamerauLevenshtein({ transpositions: false }).distance(\"ab\", \"ba\"); // 2\n```\n\n## Unicode\n\nStrings are compared by code point, so characters outside the Basic Multilingual Plane\ncount as a single character:\n\n```ts\ndistance(\"๐๐\", \"๐๐\"); // 1\n```\n\nCombining marks are _not_ normalized, so a precomposed `\"\\u00e9\"` and a decomposed\n`\"e\\u0301\"` are two different strings (distance `2`). Normalize both sides first if you\nwant them treated as equal:\n\n```ts\ndistance(\"\\u00e9\".normalize(\"NFC\"), \"e\\u0301\".normalize(\"NFC\")); // 0\n```\n\n## Which algorithm is this?\n\nThis is the **optimal string alignment** (OSA) variant of Damerau-Levenshtein, also called\nthe restricted edit distance: no substring is edited more than once. It is what most\nspell-checking and fuzzy-search code wants, and it is what the great majority of\n\"damerau-levenshtein\" packages implement.\n\nThe practical consequence is that a transposition whose characters need further editing is\nnot shared across operations:\n\n```ts\ndistance(\"a cat\", \"an act\"); // 2 โ insert \"n\", transpose \"c\" and \"a\"\ndistance(\"a cat\", \"an abct\"); // 4 โ an unrestricted implementation reports 3\n```\n\nOSA is also not a true metric: it does not satisfy the triangle inequality. Turn\ntranspositions off to get plain Levenshtein, which does.\n\nComplexity is O(nยทm) time and O(min(n, m)) memory, where n and m are the code-point lengths\nof the two strings.\n\n## Example: spelling suggestions\n\n```ts\nimport { DamerauLevenshtein } from \"@crob/damerau-levenshtein\";\n\nconst dl = new DamerauLevenshtein();\nconst dictionary = [\"apple\", \"banana\", \"orange\", \"pear\", \"peach\", \"pineapple\", \"plum\"];\n\nfunction suggest(query: string, limit = 3): string[] {\n return dictionary\n .map((word) => ({ word, score: dl.distance(query.toLowerCase(), word) }))\n .sort((a, b) => a.score - b.score)\n .slice(0, limit)\n .map(({ word }) => word);\n}\n\nsuggest(\"aplpe\"); // [\"apple\", \"plum\", \"pear\"]\n```\n\nA runnable version lives in [`example/index.html`](./example/index.html).\n\n## Migrating from 1.x\n\nVersion 2 is a breaking release. The headline change: **transpositions are now on by\ndefault**, which is what the class name and the old documentation always implied.\n\n| 1.x | 2.x |\n| ----------------------------------- | --------------------------------------------------- |\n| `new DamerauLevenshtein()` | `new DamerauLevenshtein({ transpositions: false })` |\n| `new DamerauLevenshtein({}, true)` | `new DamerauLevenshtein()` |\n| `new DamerauLevenshtein({}, false)` | `new DamerauLevenshtein({ transpositions: false })` |\n| `const DL = require(\"...\")` | `const { DamerauLevenshtein } = require(\"...\")` |\n\nPassing a second positional argument now throws with a pointer to this table, so the\nchange cannot silently alter your results.\n\nAlso worth knowing:\n\n- **Transpositions no longer switch themselves on.** In 1.x, supplying a `transpose` cost\n forced transpositions on even when they were explicitly disabled. Use `transpositions`.\n- **`transpose` argument order was fixed.** It was documented as `(backward, forward)` but\n called as `(forward, backward)`. It now matches the documentation.\n- **Custom `insert`/`remove` costs now apply to every edit.** In 1.x the first row and\n column of the distance matrix were hard-coded to 1 per character, so\n `new DamerauLevenshtein({ remove: 3 }).distance(\"abc\", \"\")` returned `3` instead of `9`.\n- **Strings are compared by code point**, not UTF-16 code unit, so distances involving\n emoji and other astral characters changed.\n- **Invalid options throw.** A misspelled option or a non-numeric cost used to be silently\n replaced with the default.\n- **Node 20.19+ is required**, and the published package now ships type declarations.\n\n## Development\n\n```sh\nnpm ci\nnpm test # vitest, including property-based tests\nnpm run test:coverage\nnpm run typecheck\nnpm run build # ESM + CJS + UMD bundles and .d.ts declarations\nnpm run lint:package\n```\n\n## Releasing\n\n1. Bump `version` in `package.json` and land it on `main`.\n2. Publish a GitHub release whose tag matches that version (`2.0.0` or `v2.0.0`).\n3. The [publish workflow](.github/workflows/publish.yml) typechecks, tests, builds, and\n verifies the tag against `package.json` before running `npm publish --provenance`.\n\nThe workflow authenticates with the `NPM_TOKEN` repository secret. Configuring\n[npm trusted publishing](https://docs.npmjs.com/trusted-publishers) for this package is\nworth doing: it drops the secret entirely in favour of the workflow's OIDC identity.\n\n## Contributing\n\nIssues and pull requests are welcome on\n[GitHub](https://github.com/chiribuc/damerau-levenshtein). Please keep the test suite green\nand run `npm run format` before opening a PR.\n\nThanks to everyone who has\n[contributed](https://github.com/chiribuc/damerau-levenshtein/graphs/contributors) โ see\nthe [changelog](./CHANGELOG.md) for what each release brought.\n\n## License\n\n[MIT](./LICENSE) ยฉ Robert-Cristian Chiribuc\n","readmeFilename":"README.md"}