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Elysia 0.2 - The Blessing

blue to purple aurora in the night sky above of snow mountain

Blessing」brings more improvement, mainly on TypeScript performance, type-inference, and better auto-completion and some new features to reduce boilerplate.

Named after YOASOBI's song「祝福」, an opening for Witch from "Mobile Suit Gundam: The Witch from Mercury".

Defers / Lazy Loading Module

With Elysia 0.2 now add support for the lazy loading module and async plugin.

This made it possible to defer plugin registration and incrementally apply after the Elysia server is started to achieve the fastest possible start-up time in Serverless/Edge environments.

To create defers module, simply mark the plugin as async:

const plugin = async (app: Elysia) => {
    const stuff = await doSomeHeavyWork()

    return app.get('/heavy', stuff)


Lazy Loading

Some modules might be heavy and importing before starting the server might not be a good idea.

We can tell Elysia to skip the module then register the module later, and register the module when finish loading by using import statement in use:


This will register the module after the import is finished making the module lazy-load.

Defers Plugin and lazy loading module will have all type-inference available right out of the box.

Reference Model

Now Elysia can memorize schema and reference the schema directly in Schema fields, without creating an import file via Elysia.setModel

This list of schema available, brings auto-completion, complete type-inference, and validation as you expected from inline schema.

To use a reference model, first, register the model with setModel, then write a model name to reference a model in schema

const app = new Elysia()
        sign: t.Object({
            username: t.String(),
            password: t.String()
    .post('/sign', ({ body }) => body, {
        schema: {
            body: 'sign',
            response: 'sign'

This will bring auto-completion of known models. Screenshot 2566-01-23 at 13 24 28

And type reference stopping you from accidentally returning invalid type. Screenshot 2566-01-23 at 13 26 00

Using @elysiajs/swagger will also create a separate Model section for listing available models. Screenshot 2566-01-23 at 13 23 41

Reference also handles validation as you expected.

In short, it's as same as inline schema but now you only need to type the name of the schema to handle validation and typing instead of a long list of imports.

OpenAPI Detail field

Introducing new field schema.detail for customizing detail for the route following the standard of OpenAPI Schema V2 with auto-completion.

Screenshot 2566-01-23 at 13 54 11

This allows you to write better documentation and fully editable Swagger as you want: Screenshot 2566-01-23 at 13 23 41

Union Type

The previous version of Elysia sometime has a problem with distinct Union types, as Elysia tries to catch the response to create a full type reference for Eden.

Results in invalidation of possible types,

Union Response

Made possible by Union Type, now returning multiple response status for schema now available using schema.response[statusCode]

        ({ body, params: { id } }) => ({
            schema: {
                body: 'sign',
                response: {
                    200: t.Object({
                        username: t.String(),
                        password: t.String(),
                        id: t.String()
                    400: t.Object({
                        error: t.String()

Elysia will try to validate all schema in response allowing one of the types to be returned.

Return types are also supported report in Swagger's response.

Faster Type Inference

As Elysia 0.1 explore the possibility of using type inference for improving better Developer Experience, we found that sometimes it takes a long time to update type inference because of heavy type inference and in-efficient custom generic.

With Elysia 0.2 now optimized for faster type-inference, preventing duplication of heavy type unwrap, results in better performance for updating type and inference.


With Elysia 0.2 enabling async plugin and deferred module many new plugins that isn't possible before became reality.


  • Elysia Static plugin with the non-blocking capability
  • Eden with union-type inference for multiple responses
  • New Elysia Apollo Plugin for Elysia

Notable Improvement:

  • onRequest and onParse now can access PreContext
  • Support application/x-www-form-urlencoded by default
  • body parser now parse content-type with extra attribute eg. application/json;charset=utf-8
  • Decode URI parameter path parameter
  • Eden now reports an error if Elysia is not installed
  • Skip declaration of existing model and decorators

Breaking Changes:

  • onParse now accepts (context: PreContext, contentType: string) instead of (request: Request, contentType: string)
    • To migrate, add .request to context to access Request


Thank you for supporting Elysia and being interested in this project.

This release brings better DX and hopefully all you need to write great software with Bun.

Now we have Discord server where you can ask any questions about Elysia or just hang out and chill around is also welcome.

With the wonderful tools, we are happy to see what wonderful software you will build.

Not to be part of those images someone paints

Not advancing in that show chosen by someone else

You and I, alive to write our story

Will never let you be lone and be gone from your side