Router Deep Dive

bunway's router uses Express-style ergonomics while staying true to Bun's Fetch APIs. This page explains the lifecycle so you can compose middleware, sub-routers, and custom responses with confidence.

Coming from Express?

If you've used Express routing, you already know bunway routing. The patterns are identical.

Anatomy of a request

1. Match – incoming requests match routes by HTTP method + path (supporting :params).
2. Pipeline – global middleware → auto body parser → route-specific middleware/handlers.
3. Execution – each handler receives (req, res, next). Call next() to continue the chain.
4. Finalization – the router chooses the final Response (explicit return, res.last, or default 200) and merges header bags (e.g., CORS) before returning.

Registering routes

Define routes using familiar HTTP verb helpers. Each handler receives the Express-compatible (req, res, next) signature:

const app = bunway();

app.get("/health", (req, res) => res.text("OK"));
app.post("/users", async (req, res) => res.created(await req.parseBody()));
app.patch("/users/:id", async (req, res) => {
  const id = req.param("id");
  const updates = await req.parseBody();
  return res.json(await updateUser(id, updates));
});

Multiple handlers

Chain middleware the same way you would in Express:

app.get("/users/:id", authMiddleware, loadUser, (req, res) => {
  res.json(req.locals.user);
});

Each handler can perform work, populate req.locals, and call next() to continue:

const authMiddleware = (req, res, next) => {
  const token = req.get("Authorization");
  if (!token) return res.unauthorized();
  req.locals.user = verifyToken(token);
  next();
};

Chainable routes

Define multiple HTTP methods on the same path without repeating yourself. This is identical to Express's app.route() pattern:

app
  .route("/users")
  .get((req, res) => res.json(allUsers))
  .post((req, res) => res.created(createUser(req.body)));

app
  .route("/users/:id")
  .get((req, res) => res.json(findUser(req.params.id)))
  .put((req, res) => res.json(updateUser(req.params.id, req.body)))
  .delete((req, res) => res.noContent());

Before (repetitive)

app.get("/users", listUsers);
app.post("/users", createUser);
app.get("/users/:id", showUser);
app.put("/users/:id", updateUser);
app.patch("/users/:id", patchUser);
app.delete("/users/:id", deleteUser);

After (chainable)

app
  .route("/users")
  .get(listUsers)
  .post(createUser);

app
  .route("/users/:id")
  .get(showUser)
  .put(updateUser)
  .patch(patchUser)
  .delete(deleteUser);

All HTTP methods

Chainable routes support all HTTP verbs:

app
  .route("/test")
  .get(handler)
  .post(handler)
  .put(handler)
  .patch(handler)
  .delete(handler)
  .options(handler)
  .head(handler)
  .all(handler); // Responds to any method

Middleware in chains

Add middleware to individual methods:

app
  .route("/admin/users")
  .get(requireAuth, listUsers)
  .post(requireAuth, requireAdmin, createUser);

Works with routers

Chainable routes work on both app and Router instances:

import { Router } from "bunway";

const api = new Router();
api
  .route("/posts")
  .get(listPosts)
  .post(authMiddleware, createPost);

app.use("/api", api);
// Routes: GET /api/posts, POST /api/posts

Middleware ordering

Global middleware runs in the order registered, followed by route-specific middleware:

app.use(cors()); // global
app.use(json()); // global
app.use(loggingMiddleware); // global

app.get("/secure", authMiddleware, (req, res) => {
  res.ok(req.locals.user);
});

• Global middleware runs before route-specific middleware.
• req.isBodyParsed() lets you skip redundant parsing.
• Middleware can return Response to short-circuit the pipeline (e.g., auth failures).

Sub-routers

Group related endpoints into sub-routers for better organization:

import { Router } from "bunway";

const api = new Router();
api.get("/users", listUsers);
api.get("/users/:id", showUser);

app.use("/api", api);

Sub-routers inherit parent middleware and can register their own router.use() handlers.

Sub-router inheritance

Middleware registered on the parent app runs before sub-router handlers. Add router-specific middleware inside the router for scoped behaviour.

Nested routers

Routers can be nested multiple levels deep:

const admin = new Router();
admin.use(requireAdmin);
admin.get("/stats", getStats);

api.use("/admin", admin);
// Full path: /api/admin/stats

mergeParams

By default, child routers do not have access to route parameters defined in the parent. Pass mergeParams: true to inherit parent params:

import { Router } from "bunway";

const userRouter = new Router({ mergeParams: true });

userRouter.get("/posts", (req, res) => {
  // req.params.userId is available from the parent mount
  res.json({ userId: req.params.userId });
});

app.use("/users/:userId", userRouter);
// GET /users/123/posts → { "userId": "123" }

Child params take precedence when the parent and child define the same parameter name.

Deep nesting works as expected — each router in the chain must have mergeParams: true to pass params through:

const orgRouter = new Router({ mergeParams: true });
const teamRouter = new Router({ mergeParams: true });

teamRouter.get("/members", (req, res) => {
  res.json({ orgId: req.params.orgId, teamId: req.params.teamId });
});

orgRouter.use("/teams/:teamId", teamRouter);
app.use("/orgs/:orgId", orgRouter);
// GET /orgs/abc/teams/xyz/members → { "orgId": "abc", "teamId": "xyz" }

Returning native responses

Handlers can always return Response objects straight from Fetch APIs—bunWay will still merge any middleware headers during finalization.

Error handling

• Throw HttpError for explicit status/body/headers.
• Throw/return Response for fully custom responses.
• Use errorHandler() middleware for logging/mapping.
• Unhandled errors fall back to a safe 500 JSON payload.

import { HttpError } from "bunway";

app.get("/secret", () => {
  throw new HttpError(403, "Forbidden");
});

404 behaviour

Unmatched routes return:

HTTP/1.1 404 Not Found
Content-Type: application/json
{"error":"Not Found"}

Customize by adding a catch-all route at the end:

app.use((req, res) => res.status(404).json({ error: "Route not found" }));

Catch-all

Be sure to register catch-all handlers last—bunway processes middleware in order, so earlier routes can short-circuit the response.

Body parser defaults

Routers accept body parser defaults via constructor:

const router = new Router({
  bodyParser: {
    json: { limit: 2 * 1024 * 1024 },
    text: { enabled: true },
  },
});

Handlers can override parsing dynamically with req.applyBodyParserOverrides().

Recipes

Request logger

app.use(async (req, res, next) => {
  const start = performance.now();
  await next();
  const ms = (performance.now() - start).toFixed(1);
  console.log(`${req.method} ${req.path} → ${res.statusCode} (${ms}ms)`);
});

Or use the built-in logger:

import { logger } from "bunway";
app.use(logger("dev"));

Admin-only sub-router

import { Router, HttpError } from "bunway";

const admin = new Router();

admin.use((req, res, next) => {
  if (req.get("Authorization") !== "super-secret") {
    throw new HttpError(401, "Admin authorization required");
  }
  next();
});

admin.get("/stats", (req, res) => {
  res.json({ uptime: process.uptime() });
});

app.use("/admin", admin);

Per-request body parser override

app.post("/webhook", async (req, res) => {
  req.applyBodyParserOverrides({ text: { enabled: true }, json: { enabled: false } });
  const payload = await req.parseBody();
  return res.ok({ received: payload });
});

Advanced patterns

• Streaming: work directly with await req.rawBody() or req.original.body for streams.
• Locals: share data across middleware via req.locals (e.g., req.locals.user = user).
• Async cleanup: run code after await next() to implement logging, timers, or metrics.

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Continue to Middleware Overview or explore type-level details in the API Reference.