🌳 rou3

Lightweight and fast router for JavaScript.

Usage

Install:

# ✨ Auto-detect
npx nypm install rou3

Import:

ESM (Node.js, Bun, Deno)

import {
  createRouter,
  addRoute,
  findRoute,
  removeRoute,
  findAllRoutes,
  routesOverlap,
  compareRoutes,
  findOverlappingRoutes,
  routeToRegExp,
  regExpToRoute,
  NullProtoObj,
} from "rou3";

CDN (Deno and Browsers)

import {
  createRouter,
  addRoute,
  findRoute,
  removeRoute,
  findAllRoutes,
  routesOverlap,
  compareRoutes,
  findOverlappingRoutes,
  routeToRegExp,
  regExpToRoute,
  NullProtoObj,
} from "https://esm.sh/rou3";

Create a router instance and insert routes:

import { createRouter, addRoute } from "rou3";

const router = createRouter(/* options */);

addRoute(router, "GET", "/path", { payload: "this path" });
addRoute(router, "POST", "/path/:name", { payload: "named route" });
addRoute(router, "GET", "/path/foo/**", { payload: "wildcard route" });
addRoute(router, "GET", "/path/foo/**:name", {
  payload: "named wildcard route",
});

Match route to access matched data:

// Returns { payload: 'this path' }
findRoute(router, "GET", "/path");

// Returns { payload: 'named route', params: { name: 'fooval' } }
findRoute(router, "POST", "/path/fooval");

// Returns { payload: 'wildcard route' }
findRoute(router, "GET", "/path/foo/bar/baz");

// Returns undefined (no route matched for/)
findRoute(router, "GET", "/");

Match all routes, ordered least → most specific:

findAllRoutes(router, "GET", "/path/foo/bar/baz");
// [
//   { data: { payload: "wildcard route" } },
//   { data: { payload: "named wildcard route" }, params: { name: "bar/baz" } },
// ]

The result ordering is a documented contract — see Result ordering.

Route Patterns

rou3 supports URLPattern-compatible syntax.

Pattern	Example Match	Params
/path/to/resource	/path/to/resource	{}
/users/:name	/users/foo	{ name: "foo" }
/path/**	/path/foo/bar	{}
/path/**:rest	/path/foo/bar	{ rest: "foo/bar" }
/files/*.png	/files/icon.png	{ "0": "icon" }
/files/file-*-*.png	/files/file-a-b.png	{ "0": "a", "1": "b" }
/users/:id(\\d+)	/users/123	{ id: "123" }
/files/:ext(png|jpg)	/files/png	{ ext: "png" }
/path/(\\d+)	/path/123	{ "0": "123" }
/users/:id?	/users or /users/123	{} or { id: "123" }
/files/:path+	/files/a/b/c	{ path: "a/b/c" }
/files/:path*	/files or /files/a/b	{} or { path: "a/b" }
/book{s}?	/book or /books	{}
/blog/:id(\\d+){-:title}?	/blog/123 or /blog/123-my-post	{ id: "123" } or { id: "123", title: "my-post" }

• Named params (:name) match a single segment.
• Single-segment wildcards (*) capture unnamed params (0, 1, ...) and can be used as full or mid-segment tokens (for example /* or /*.png).
• Wildcards (**) match zero or more segments. Use **:name to capture.
• Regex constraints (:name(regex)) restrict matching. Constrained and unconstrained params can coexist on the same node (constrained checked first).
• Unnamed groups ((regex)) capture into auto-indexed keys 0, 1, etc.
• Modifiers: :name? (optional), :name+ (one or more), :name* (zero or more). Can combine with regex: :id(\d+)?.
• Non-capturing groups ({...}): supported with inline (/foo{bar}) and optional (/foo{bar}?) forms.
• Current limitation: repeating non-capturing groups ({...}+, {...}*) are supported only within a single segment (no / inside the group body).
• Backslash escaping (\): escape special characters like :, *, (, ), {, } with a backslash (e.g., /static\:path matches literal /static:path).

Differences from URLPattern

rou3 aims for URLPattern-compatible syntax but has intentional differences due to its radix-tree design:

Feature	URLPattern	rou3
* (single star)	Greedy catch-all (.*) across /	Single-segment unnamed param ([^/]*)
** (double star)	Literal **	Catch-all wildcard (zero or more segments)
(.*) in segment	Greedy match across /	Segment-scoped (does not cross /)
{...}+ / {...}* groups	Cross-segment group repetition	Only supported within a single segment (no / in group body)
Path normalization (./..)	Resolves ./.. in input paths	Not done by default (opt-in with { normalize: true })
Case sensitivity	Can be case-insensitive	Always case-sensitive
Non-/-prefixed paths	Supported	Paths must start with /
Unicode param names	Supports Unicode identifiers	Params use \w (ASCII word chars only)
Percent-encoding	Normalizes %xx sequences	Does not decode percent-encoded input

Path normalization

By default, findRoute and findAllRoutes do not resolve ./.. segments in input paths. If your input paths may contain relative segments, enable normalization:

findRoute(router, "GET", "/foo/bar/../baz", { normalize: true });
// Matches "/foo/baz"

findAllRoutes(router, "GET", "/foo/./bar", { normalize: true });
// Matches "/foo/bar"

The compiled router also supports this via the normalize option:

const match = compileRouter(router, { normalize: true });
match("GET", "/foo/bar/../baz"); // Matches "/foo/baz"

Result ordering

findAllRoutes returns matches ordered least → most specific: the broadest scopes first, the most specific match last. The compiled matchAll (see Compiler) returns the exact same results in the exact same order. This ordering is a contract, not incidental behavior — merge/fold-style consumers (e.g. route rules resolved by merging all matched layers, taking the last as the most specific) can rely on it, and it is pinned by tests. Any intentional change to it would be a breaking change.

const router = createRouter();
addRoute(router, "GET", "/**", { name: "catch-all" });
addRoute(router, "GET", "/api/**", { name: "api" });
addRoute(router, "GET", "/api/:v/users/:id", { name: "user" });

findAllRoutes(router, "GET", "/api/v1/users/42").map((m) => m.data.name);
// ["catch-all", "api", "user"]

Precisely:

• Across the tree: at each level, wildcard (**) matches are emitted first, then single-segment params (*, :name), then static segments — so wilder/shallower routes come before more-static/deeper ones.
• Same-node siblings (multiple routes ending on the same dynamic node, e.g. /foo/* and /foo/:id(\d+)): ordered by ascending specificity — optional/unconstrained entries before required/regex-constrained ones — with insertion order preserved on ties.
• Subsumption consistency: when registered patterns are strictly ordered by containment (each a "superset" of the next per compareRoutes), the result order agrees with the subsumption order (broader first).
• Registration order never affects the result order, except as the tiebreaker between equally specific same-node siblings.

findOverlappingRoutes follows the same least → most specific order.

Pattern overlap

findRoute/findAllRoutes match a concrete path against registered patterns. Sometimes you instead need to reason about patterns against patterns — e.g. to resolve an "effective" merged config over a whole scope, you need to know when two patterns can match a common concrete path.

Three utilities cover this:

import { createRouter, addRoute, routesOverlap, compareRoutes, findOverlappingRoutes } from "rou3";

// Do two patterns share at least one concrete path? (pure, router-free)
routesOverlap("/**", "/protected/feed/**"); // true
routesOverlap("/a/**", "/b/**"); // false

// How do two patterns' match-sets relate? (pure, router-free)
compareRoutes("/api/**", "/api/admin/**"); // "superset"
compareRoutes("/api/admin/**", "/api/**"); // "subset"
compareRoutes("/a/:x", "/a/:y"); // "equal" (names don't matter)
compareRoutes("/a/*/c", "/a/b/*"); // "partial" (ambiguous specificity)

// Every registered route whose match-set intersects a *pattern* (a scope),
// ordered least -> most specific like findAllRoutes.
const router = createRouter();
addRoute(router, "GET", "/**", { isr: true });
addRoute(router, "GET", "/protected/**", { basicAuth: true });
addRoute(router, "GET", "/protected/feed/**", { isr: 60 });

findOverlappingRoutes(router, "GET", "/protected/feed/**");
// [ { data: { isr: true } },        // /**
//   { data: { basicAuth: true } },  // /protected/**
//   { data: { isr: 60 } } ]         // /protected/feed/**

• routesOverlap(patternA, patternB) — returns true if the two patterns' match-sets intersect (there exists a concrete path matched by both). This is overlap, not subset containment.

• compareRoutes(patternA, patternB) — classifies the relation between the two match-sets. Verdicts follow the ES2025 Set-method vocabulary (isSupersetOf/isSubsetOf/isDisjointFrom) and are directional — read them as "patternA is a … of patternB":

  • "disjoint" — provably no common path.
  • "equal" — provably the same paths. Param names are ignored: /a/:x equals /a/:y, /u/:id(\d+) equals /u/:x(\d+), and /a/:x? equals /a/*.
  • "superset" — patternA provably matches every path patternB matches (strict unless equality is undecidable).
  • "subset" — the mirror image (patternA ⊆ patternB).
  • "partial" — no containment proven; the sets may intersect.

  Useful for ordering patterns by specificity and detecting ambiguous pairs where "most specific match" is undefined. Every verdict's containment claims are proofs, and undecidable cases degrade to a weaker verdict, never a wrong claim: containment between two different regex constraints falls back to "partial" (even when the sets are actually disjoint — see the over-approximation note below — or actually equal), and an actually-equal pair whose equality is only provable in one direction (e.g. /u/:id(42) vs /u/42) reports the proven containment instead of "equal".

• findOverlappingRoutes(router, method, pattern) — like findAllRoutes, but the query is a pattern instead of a concrete path. Returns every registered route whose match-set intersects the pattern, ordered least → most specific, with the same method handling as findAllRoutes (falls back to the method-agnostic bucket). Matches carry only data — a scope has no single concrete path, so no params are resolved. A single route registered with optional/group syntax expands into several tree entries sharing one data reference and is reported once; distinct routes are always reported separately, even when they share an equal primitive data value (or none).

Overlap semantics are computed with rou3's own segment/radix rules, so they stay consistent with findRoute/findAllRoutes:

• Patterns are expanded through the same pipeline as addRoute, so groups ({s}?), optional/repeat modifiers (:x?/:x+/:x*), and escaping (\:, \*) are all respected. A pattern with optional syntax expands to several shapes; two patterns overlap when any pair of shapes overlaps.
• Segment counts: bare ** matches zero or more segments (so /a/** overlaps /a), **:name matches one or more, a trailing bare * matches zero or one, and mid-pattern * / :name match exactly one.
• Regex constraints (:id(\d+), unnamed groups, *.png) are matched precisely against static literals (/user/:id(\d+) does not overlap /user/abc), but two dynamic segments where at least one is constrained are over-approximated to "overlaps" — routesOverlap("/user/:id(\d+)", "/user/:name([a-z]+)") returns true even though the sets are disjoint. Exact regex intersection is undecidable, and over-approximating toward "overlaps" is the safe conservative default.

Regular expressions

routeToRegExp(route) converts a route pattern into an anchored RegExp with named capture groups, useful outside the router (validation, codegen, matching in other tools):

import { routeToRegExp } from "rou3";

routeToRegExp("/users/:id(\\d+)");
// /^\/users\/(?<id>\d+)\/?$/  ->  "/users/123".match(re).groups // { id: "123" }

The output is PCRE-compatible: it uses (?<name>...) named groups and avoids JS-only constructs, so the generated .source also compiles in PCRE2 engines (grep -P, rg -P, pcre2grep, PHP preg_*) and Perl — not just JavaScript. In particular, trailing optional groups are compiled inline as (?:...)? instead of an alternation, so a param is never emitted twice as a duplicate named group (which PCRE2 rejects unless PCRE2_DUPNAMES is set):

routeToRegExp("/blog/:id(\\d+){-:title}?");
// /^\/blog\/(?<id>\d+)(?:-(?<title>[^/]+))?\/?$/

regExpToRoute(regexp) is the inverse: it parses an anchored, PCRE-compatible RegExp (or its source string) back into a route pattern. Pass either a RegExp or a source string:

import { regExpToRoute } from "rou3";

regExpToRoute(/^\/users\/(?<id>\d+)\/?$/); // "/users/:id(\\d+)"
regExpToRoute(/^\/path\/(?<param>[^/]+)\/?$/); // "/path/:param"
regExpToRoute(/^\/base\/?(?<path>.+)\/?$/); // "/base/**:path"
regExpToRoute("^\\/files\\/(?<_0>[^/]*)\\.png\\/?$"); // "/files/*.png"

It targets the dialect routeToRegExp() emits — named groups (?<name>...), [^/]+/[^/]* segment matchers, .*/.+ catch-alls, and (?:/...)? optional groups. Bare (unnamed) capturing groups such as (\d+) are accepted too, and arbitrary regex inside an inline constraint (...) is preserved verbatim. Every reversible output round-trips exactly: routeToRegExp(regExpToRoute(regexp)).source === regexp.source.

Anything outside that dialect throws a clear error rather than returning a corrupt pattern: structural look-arounds ((?=…), (?<=…)) and backreferences, bare regex operators outside a constraint (|, ., +, […], …), match-affecting flags (i/m/s), the non-reversible alternation fallback described above, and inline constraints that can't be expressed as a route (e.g. one containing /).

Compiler

compileRouter(router, opts?)

Compiles the router instance into a faster route-matching function.

IMPORTANT: compileRouter requires eval support with new Function() in the runtime for JIT compilation.

Example:

import { createRouter, addRoute } from "rou3";
import { compileRouter } from "rou3/compiler";
const router = createRouter();
// [add some routes]
const findRoute = compileRouter(router);
const matchAll = compileRouter(router, { matchAll: true });
findRoute("GET", "/path/foo/bar");

compileRouterToString(router, functionName?, opts?)

Compile the router instance into a compact runnable code.

IMPORTANT: Route data must be serializable to JSON (i.e., no functions or classes) or implement the toJSON() method to render custom code or you can pass custom serialize function in options.

Example:

import { createRouter, addRoute } from "rou3";
import { compileRouterToString } from "rou3/compiler";
const router = createRouter();
// [add some routes with serializable data]
const compilerCode = compileRouterToString(router, "findRoute");
// "const findRoute=(m, p) => {}"

License

Published under the MIT license. Made by @pi0 and community 💛

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