zemi

zemi is a data-driven routing library for Express, built with Typescript.

Features:

• reverse-routing
• path-parameter inheritance
• route-level middleware support

Table of Contents

1. Routing
   1. Data-driven
   2. Reverse-routing
   3. Middleware
   4. Parameter Inheritance
2. Types
   1. ZemiMethod
   2. ZemiRequestHandler
   3. ZemiRequest
   4. ZemiResponse
   5. ZemiRouteDefinition
   6. ZemiRoute
3. Examples
   1. Simple
   2. With Middleware
   3. Using Named Routes For Redirects
   4. Using Reverse Routing
   5. With Param Inheritance from Parent Routes
4. Limitations

Routing

Data-driven

Assume you have the following functions defined: petsHandler, dogBreedHandler, dogBreedsIdHandler, catsByIdHandler ; e.g.:

const petsHandler = (request: ZemiRequest, response: ZemiResponse) => {
  // do something with this request and respond
  response.status(200).json({ pets: ["dogs", "cats"] });
};

const dogBreedHandler = (request: ZemiRequest, response: ZemiResponse) => {
   //...
};

const dogBreedsIdHandler = (request: ZemiRequest, response: ZemiResponse) => {
   //...
};

const catsByIdHandler = (request: ZemiRequest, response: ZemiResponse) => {
   //...
};

Then the following code:

import express from "express";
import zemi, { ZemiRoute, ZemiMethod } from "zemi";

const { GET } = ZemiMethod;

const routes: Array<ZemiRoute> = [
  {
    name: "pets",
    path: "/pets",
    [GET]: petsHandler,
    routes: [
      {
        name: "dogBreeds",
        path: "/dogs/:breed",
        [GET]: dogBreedHandler,
        routes: [
          {
            name: "dogsByBreedById",
            path: "/:id",
            [GET]: dogBreedsIdHandler
          }
        ]
      },
      {
        name: "catsById",
        path: "/cats/:id",
        [GET]: catsByIdHandler
      }
    ]
  }
];

const app = express();
app.use(express.json());
app.use("/", zemi(routes));
app.listen(3000);

Generates an API like:

routes	response
/pets	{pets: ['dogs', 'cats', 'rabbits']}
/pets/dogs	Cannot GET /pets/dogs/ (since it was not defined)
/pets/dogs/labrador	{"result":["Fred","Barney","Wilma"]}
/pets/dogs/labrador/1	{"result":"Barney"}
/pets/cats	Cannot GET /pets/cats/ (since it was not defined)
/pets/cats/2	{"result":"Daphne"}

Reverse-routing

zemi builds route-definitions for all routes and adds them to the ZemiRequest passed to the handler function.

All route-definitions are named (index-accessible) and follow the same naming convention: [ancestor route names]-[parent route name]-[route name], e.g. basePath-greatGrandparent-grandparent-parent-myRoute, pets-dogsBreeds-dogsByBreedById.

Each route-definition contains the name, path, and path-parameters (if present) of the route. It also contains a reverse function which — when invoked with an object mapping path-parameters to values — will return the interpolated path with values.

E.g. a handler like this:

import { ZemiRequest, ZemiResponse, ZemiRouteDefinition } from "zemi";

const petsHandler = (request: ZemiRequest, response: ZemiResponse) => {
  const routeDefinitions: Record<string, ZemiRouteDefinition> = request.routeDefinitions;
  const { path, name, parameters, reverse } = routeDefinitions["pets-dogBreeds-dogsByBreedById"];
  response.status(200).json({ path, name, parameters, reverse: reverse({ breed: 'Corgi', id: '99' }) });
};

Returns:

  {
  "path": "/pets/dogs/:breed/:id",
  "name": "pets-dogBreeds-dogsByBreedById",
  "parameters": [
    "breed",
    "id"
  ],
  "reverse": "/pets/dogs/corgi/99"
}

This allows you to generate links, redirect, and change path values without having to hardcode strings and change them later.

Middleware

zemi lets you define middleware functions at the route level:

Retaking and tweaking our example from the beginning:

import { ZemiRequest, ZemiResponse } from "zemi";
import { NextFunction } from "express";

const routes: Array<ZemiRoute> = [
  {
    name: "pets",
    path: "/pets",
    [GET]: petsHandler,
    routes: [
      {
        name: "dogBreeds",
        path: "/dogs/:breed",
        [GET]: dogBreedHandler,
        middleware: [
          function logRouteDefs(request: ZemiRequest, response: ZemiResponse, next: NextFunction) {
            console.log(JSON.stringify(request.routeDefinitions));
            next();
          }
        ],
        routes: [
          {
            name: "dogsByBreedById",
            path: "/:id",
            [GET]: dogBreedsIdHandler
          }
        ]
      },
      {
        name: "catsById",
        path: "/cats/:id",
        [GET]: { handler: catsByIdHandler }
      }
    ]
  }
];

The middleware function logRouteDefs defined at the dogBreeds level will be applied to all the methods at that level and all nested routes — which means our dogsByBreedById route will gain that functionality also.

Parameter Inheritance

As show in previous examples, parameters defined at parent routes are passed and available to nested routes.

E.g. in this purposefully convoluted example:

const routes: Array<ZemiRoute> = [
  {
    name: "pets",
    path: "/pets",
    [GET]: petsHandler,
    routes: [
      {
        name: "dogBreeds",
        path: "/dogs/:breed",
        [GET]: dogBreedHandler,
        routes: [
          {
            name: "dogsByBreedById",
            path: "/:id",
            [GET]: dogBreedsIdHandler,
            routes: [
              {
                name: "dogsByBreedByIdDetailsSection",
                path: "/details/:section",
                [GET]: dogBreedsIdDetailsSectionHandler,
                routes: [
                  {
                    name: "newDogsByBreedByIdDetailsSection",
                    path: "/new",
                    [POST]: newDogsByBreedByIdDetailsSectionHandler
                  }
                ]
              }
            ]
          }
        ]
      }
    ]
  }
];

The newDogsByBreedByIdDetailsSection route (path: /pets/dogs/:breed/:id/details/:section/new) will have breed, id, and section available as request parameters in the ZemiRequest object.

Types

ZemiMethod

Enum

The HTTP methods supported by ZemiRoute.

Member	Value
GET	get
POST	post
PUT	put
DELETE	delete
OPTIONS	options

ZemiRequestHandler

How to handle incoming requests for this route method; basically express.RequestHandler, but gets passed its own request and response versions, plus adds that routes ZemiRouteDefinition as an optional fourth param.

(
  request: ZemiRequest,
  response: ZemiResponse,
  next: express.NextFunction,
  routeDef: ZemiRouteDefinition
) => void

ZemiRequest

extends express.Request

A wrapper for express.Request; adds routeDefinitions and allowedResponseHttpCodes to it.

{
  routeDefinitions: Record<string, ZemiRouteDefinition>;
  // all other members from express.Request
}

ZemiResponse

extends express.Response

Just a wrapper for future-proofing; same as express.Response.

ZemiRouteDefinition

Route definition for a given ZemiRoute. Contains the name, path, and path-parameters (if present) of the route it's defining. Also provides a reverse function that, when invoked with an object that has parameter-values, will return the resolved path.

{
  name: string;
  path: string;
  parameters: Array<string>;
  reverse: (parameterValues: object) => string;
}

ZemiRoute

It must be provided a name: string and path: string; a ZemiMethod:ZemiHandlerDefinition needs to be provided if that path should have functionality, but doesn't need to be if the path is just present as a path-prefix for nested routes.

{
   [ZemiMethod]: ZemiHandlerDefinition;
   name: string;
   path: string;
   middleware?: Array<RequestHandler>;
   routes?: Array<ZemiRoute>;
}

Examples

Examples are available in the examples dir:

1. Simple

2. With Middleware

3. Using Named Routes For Redirects

4. Using Reverse Routing

5. With Param Inheritance from Parent Routes

Limitations

zemi is a recursive library: it uses recursion across a number of operations in order to facilitate a low footprint and straightforward, declarative definitions.

Recursive operations can break the call-stack by going over its limit, generating Maximum call stack size exceeded errors. This means that the recursive function was called too many times, and exceeded the limit placed on it by Node.

While recursive functions can be optimized via tail call optimization (TCO), that feature has to be present in the environment being run for optimization to work.

Unfortunately — as of Node 8.x — TCO is no longer supported.

This means that, depending on what you're building and the size of your API, zemi might not be the right fit for you. zemi uses recursion when dealing with nested routes, so if your application has a very high number of nested-routes within nested-routes, chances are you might exceed the call stack.