Elysia in 100 Seconds

Source: Dev.to

Overview

ElysiaJS is a high‑performance, statically typed web framework that runs on the Bun runtime. It is known for being significantly faster than Express and aims to provide a developer‑friendly API while retaining raw speed.

Features

• Speed – Leverages Bun’s Just‑In‑Time compiler for microsecond‑level startup times.
• Type safety – Uses TypeBox to provide end‑to‑end type safety without runtime performance penalties or extensive boilerplate.
• Fluent API – Routes are defined with a chainable syntax (.get(), .post(), etc.) that returns plain objects automatically serialized to JSON.
• Schema validation – Attach a schema object via the t variable to validate incoming data at runtime and infer TypeScript types for IDE autocompletion.
• Eden Treaty – Allows the frontend to import backend type definitions directly, giving full autocompletion for API calls on the client side.
• Minimal decorators – Unlike NestJS, Elysia does not require complex decorator usage to define routes.

Getting Started

1. Install Bun (if you haven’t already).

2. Create a TypeScript file (e.g., app.ts).

3. Initialize the app:

   import { Elysia, t } from "elysia";
   
   const app = new Elysia();

4. Define a route using the fluent API:

   app.get("/", () => {
     return { message: "Hello, Elysia!" };
   });

5. Add schema validation (optional but recommended):

   app.get(
     "/user/:id",
     {
       params: t.Object({
         id: t.String(),
       }),
     },
     ({ params }) => {
       // `params.id` is guaranteed to be a string
       return { userId: params.id };
     }
   );

6. Run the server:

   bun run app.ts

   The server will start up in microseconds, ready to handle requests.

Summary

ElysiaJS combines the speed of Bun with robust type safety and a concise, chainable API, making it a compelling alternative to traditional Node.js frameworks like Express and NestJS. Its built‑in schema validation and Eden Treaty further streamline full‑stack development by keeping backend and frontend type definitions in sync.