_Elysia_Framework_for_Bun

Updated 2026-05-16

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Elysia is an ergonomic, high-performance TypeScript web framework built for Bun that delivers exceptional speed (255k+ requests/second), end-to-end type safety with automatic inference, and seamless integration with the Bun runtime. The framework combines a developer-friendly API with powerful features like automatic OpenAPI generation, lifecycle hooks, plugin architecture, and Eden Treaty for type-safe client-server communication—all while requiring minimal TypeScript boilerplate.

What This Cheat Sheet Covers

This topic spans 15 focused tables and 208 indexed concepts, 147 flashcards. Below is a complete table-by-table outline of this topic, spanning foundational concepts through advanced details.

Table 1: Installation & Quick StartTable 2: Basic Routing & Path ParametersTable 3: Handler Context & UtilitiesTable 4: Request Validation (Schema Builder)Table 5: Lifecycle Hooks & EventsTable 6: Plugin System & Dependency InjectionTable 7: Cookie & Session ManagementTable 8: WebSocket ImplementationTable 9: Eden Treaty (End-to-End Type Safety)Table 10: Error Handling & ValidationTable 11: OpenAPI & DocumentationTable 12: Official Plugins (Common Use Cases)Table 13: Testing PatternsTable 14: Performance OptimizationTable 15: Deployment & Production

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Table 1: Installation & Quick Start

Getting from nothing to a running server is famously short with Elysia—install Bun, scaffold a project, and you have a typed HTTP server listening on a port in a handful of lines. These entries cover that first stretch: installing the runtime, chaining your first routes, configuring the listener, and reading back the underlying Bun server so you know exactly what you've started.

Feature	Example	Description
Install Bun Runtime	`curl -fsSL \| bash`	• JavaScriptruntime optimized for performance • required to run Elysia at full speed • Alternative: use with Node.js using polyfills
Create New Project	`bun create elysia app`	• Scaffolds new Elysia project with automatic setup • Navigate to directory with `cd app` after creation
Basic Server Setup	`import { Elysia } from 'elysia'` `new Elysia().get('/', 'Hello').listen(3000)`	Minimal Elysia server listening on port 3000. Returns "Hello" for GET / requests.
Development Server	`bun dev`	• Starts development server with hot-reload on file changes • Automatically restarts on code modifications
Multiple Routes	`new Elysia()` `.get('/', 'Hello')` `.post('/user', ({body}) => body)` `.listen(3000)`	• Chain multiple route handlers • Supports GET, POST, PUT, PATCH, DELETE, and custom HTTP methods
TypeScript Auto-Inference	`new Elysia()` `.get('/:id', ({params: {id}}) => id)`	Automatically infers types from route patterns without manual type declarations. `id` is typed as string.
Listen Configuration	`.listen({` `port: 3000,` `hostname: '0.0.0.0'` `})`	• Configure server port and hostname • Supports callback for server start confirmation
Environment Port	`.listen(process.env.PORT ?? 3000)`	Use environment variable for port (required for platforms like Railway). Falls back to 3000 in development.
Check Server Info	`const app = new Elysia().listen(3000)` `console.log(app.server)`	• Access underlying Bun server instance • Provides hostname, port, and other server details
Graceful Shutdown	`const app = new Elysia().listen(3000)` `app.stop()`	• Properly close server connections • Returns void when shutdown completes

Table 2: Basic Routing & Path Parameters

Routing is the spine of any web framework, and Elysia keeps it expressive: static paths, dynamic :id segments, wildcards, and grouped prefixes all chain off a single instance. Pay attention to the priority rule near the end—static beats dynamic beats wildcard—because it's what lets /user/admin and /user/:id coexist without surprises.

Feature	Example	Description
Static Routes	`.get('/user', () => 'User list')` `.post('/user', handler)`	• Define static path routes • First parameter is path, second is handler function

The rest of this section is part of the full cheat sheet

Table 3: Handler Context & Utilities

Every handler receives a single destructured context object, and these rows are the menu of what you can pull out of it—body, query, params, headers, cookies, and shared store on the way in; set, status, redirect, and streaming helpers on the way out. Learning this object well is most of what makes day-to-day Elysia productive.

Feature	Example	Description
Request Body	`({body}) => body`	• Access parsed request body • Automatically parsed based on Content-Type (JSON, FormData, Text).

The rest of this section is part of the full cheat sheet

Table 4: Request Validation (Schema Builder)

Validation is where Elysia's type story pays off: declare a schema with Elysia.t (its TypeBox builder) and you get both a runtime 400-on-failure guard and automatically inferred TypeScript types for free, with no separate type declarations. The rows walk through validating each part of a request—body, query, params, headers, cookies, files—plus coercion, optional and default fields, custom error messages, and even response-shape validation per status code. Standard Schema support means you can swap in Zod, Valibot, or ArkType if you prefer.

Feature	Example	Description
Elysia.t (TypeBox)	`import {Elysia, t} from 'elysia'`	• Built-in schema builder based on TypeBox • Validates runtime and provides compile-time types

The rest of this section is part of the full cheat sheet

Table 1: Installation & Quick Start

Feature	Example	Description
Install Bun Runtime	`curl -fsSL \| bash`	• JavaScriptruntime optimized for performance • required to run Elysia at full speed • Alternative: use with Node.js using polyfills
Create New Project	`bun create elysia app`	• Scaffolds new Elysia project with automatic setup • Navigate to directory with `cd app` after creation
Basic Server Setup	`import { Elysia } from 'elysia'` `new Elysia().get('/', 'Hello').listen(3000)`	Minimal Elysia server listening on port 3000. Returns "Hello" for GET / requests.
Development Server	`bun dev`	• Starts development server with hot-reload on file changes • Automatically restarts on code modifications
Multiple Routes	`new Elysia()` `.get('/', 'Hello')` `.post('/user', ({body}) => body)` `.listen(3000)`	• Chain multiple route handlers • Supports GET, POST, PUT, PATCH, DELETE, and custom HTTP methods
TypeScript Auto-Inference	`new Elysia()` `.get('/:id', ({params: {id}}) => id)`	Automatically infers types from route patterns without manual type declarations. `id` is typed as string.
Listen Configuration	`.listen({` `port: 3000,` `hostname: '0.0.0.0'` `})`	• Configure server port and hostname • Supports callback for server start confirmation
Environment Port	`.listen(process.env.PORT ?? 3000)`	Use environment variable for port (required for platforms like Railway). Falls back to 3000 in development.
Check Server Info	`const app = new Elysia().listen(3000)` `console.log(app.server)`	• Access underlying Bun server instance • Provides hostname, port, and other server details
Graceful Shutdown	`const app = new Elysia().listen(3000)` `app.stop()`	• Properly close server connections • Returns void when shutdown completes

Table 2: Basic Routing & Path Parameters

Feature	Example	Description
Static Routes	`.get('/user', () => 'User list')` `.post('/user', handler)`	• Define static path routes • First parameter is path, second is handler function

Table 3: Handler Context & Utilities

Feature	Example	Description
Request Body	`({body}) => body`	• Access parsed request body • Automatically parsed based on Content-Type (JSON, FormData, Text).

Table 4: Request Validation (Schema Builder)

Feature	Example	Description
Elysia.t (TypeBox)	`import {Elysia, t} from 'elysia'`	• Built-in schema builder based on TypeBox • Validates runtime and provides compile-time types

Elysia Framework for Bun Cheat Sheet

Table 1: Installation & Quick Start

Table 2: Basic Routing & Path Parameters

Table 3: Handler Context & Utilities

Table 4: Request Validation (Schema Builder)

Elysia Framework for Bun Cheat Sheet

Table 1: Installation & Quick Start

Table 2: Basic Routing & Path Parameters

Table 3: Handler Context & Utilities

Table 4: Request Validation (Schema Builder)