Narcissistic, Perfectly Modest

    TypeScript icon, indicating that this package has built-in type declarations

    0.1.1 • Public • Published

    Omicron - Simple HTTP servers

    coverage report pipeline status

    Omicron is a small library to build HTTP servers in Node.js in a more functional way.

    Omicron uses a more functional approach compared to other solutions.

    In Omicron every route handler you implement is just a basic function that eventually receives a req: HttpRequest object or in the case of an error handler also an Error. The handler function just returns the data that will be sent back to the client.

    This allows you to do things like function composition and other powerful stuff with your handlers. For example when you use middlewares with useMiddleware() it composes the middleware functions with your normal handler function.

    Omicron is written in TypeScript and has pretty good typing, which should help you to be more productive.

    Please see /example/example.ts for an example setup.


    npm i --save @zaetrik/omicron

    For some features, like middlewares, you also need the fp-ts library.

    npm i --save fp-ts


    Start a server that handles a GET request to / =>

    import * as omicron from "@zaetrik/omicron";
    const indexHandler = r
        ((req) => "Hello 👋")
        ((req, error) => `Oops! An error occured => ${error.message}`);
    const listener = omicron.httpListener({
        // Here you can add all your routes that should be exposed
        routes: [
    const PORT = 3000; // Otherwise the default PORT is 7777
    // Create our server instance
    const server = omicron.createServer({ port: PORT, listener: listener });
    // await our server setup with await server
    const main: IO<void> = async () => await (await server)();
    // Call main() to start the server
    console.log(`Listening on https://localhost:${PORT || 7777}`)

    Route Handlers 🛤️

    Route handlers can be created like this =>

    import * as omicron from "@zaetrik/omicron";
    const handler = omicron.r
        ("/") // Your path
        ("*") // HTTP method // * => Catch-all handler
        ((req) => "My Handler") // Handler function
        ((req, err) => err.message) // Error handler function
    const getHandler = omicron.get
        ((req) => "My GET Handler")
        ((req, err) => err.message)
    const postHandler =
        ((req) => "My POST Handler")
        ((req, err) => err.message)
    // To return a response with custom options you have to return something of type RouteResponse
    interface RouteResponse {
        response: any;
        status: number;
        headers: RouteResponseHeaders;
    // If you would like to just return the default headers set headers to {}
    const handlerWithCustomOptions = omicron.r
        ((req) =>
                response: "My Handler Response", // Data that should be returned as a response
                status: 200, // Custom status code
                headers: { "Set-Cookie": ["cookie=true"] } // Pass in all your custom headers
        ((req, err) => err.message)

    For the other HTTP methods there are also handlers available.

    In order for your route to work you have to define two handlers. One normal handler & one error handler. This forces you to handle the possible error scenario on every route.

    Middleware 🖖

    import * as omicron from "@zaetrik/omicron";
    import * as E from "fp-ts/lib/Either";
    import { flow } from "fp-ts/lib/function";
    // This is how you can create middleware
    const authenticated: omicron.Middleware = (req: omicron.HttpRequest) =>
        req.query.number > 10 ? E.right(req) : E.left(new Error("Number is not > 10"));
    const isBob: omicron.Middleware = (req: omicron.HttpRequest) => === "Bob" ? E.right(req) : E.left(new Error("User is not Bob"));
    const handlerWithMiddleware = omicron.r
                ((req) => "User is authenticated"))
        ((req, err) => err.message);
    const handlerWithMultipleMiddlewares = omicron.r
            // Middlewares are executed from left to right
            ([authenticated, isBob])
            ((req) => "User is authenticated and his name is Bob"))
        ((req, err) => err.message);

    As you can see we use the useMiddleware([middleware])(handler)(errorHandler?) function instead of a basic handler function we use normally. Any middleware function has to return something of type Either<Error, HttpRequest | unknown> (Either is a type from fp-ts).

    The default behaviour of the middleware is to throw the error in the handler and then you should handle it in your error handler like you always do. Another option is to pass an additional error handler to useMiddleware()()(errorHandler) which will handle any error from the middleware.

    The value returned from the middleware is used as the first parameter of your handler function, which is normally the req: HttpRequest object, but it could be whatever you like.

    Another way of creating and using middleware is this =>

    import * as omicron from "@zaetrik/omicron";
    const authenticatedErrorThrowing: omicron.ErrorThrowingMiddleware = (req: HttpRequest) =>
        req.query.number > 10
            ? req
            : (() => {
                throw new Error("Number is not > 10");
    const isBobErrorThrowing: omicron.ErrorThrowingMiddleware = (req: omicron.HttpRequest) => === "Bob"
            ? req
            : (() => {
                throw new Error("User is not Bob");
    const handlerWithErrorThrowingMiddlewares = omicron.r
            ([authenticatedErrorThrowing, isBobErrorThrowing])
            ((req) => "User is authenticated and his name is Bob"))
        ((_, err) => err.message);

    You also have the option to create middleware that just returns the raw value. Middleware of type ErrorThrowingMiddleware has to return either the raw value, that should be passed to the next middleware or the route handler, or it has to throw an error, which will then be passed to your error handler.

    Error throwing middleware can only be used with useErrorThrowingMiddleware().


    npm i @zaetrik/omicron

    DownloadsWeekly Downloads






    Unpacked Size

    61.2 kB

    Total Files


    Last publish


    • zaetrik