Elysia Tutorial

We will be building a small CRUD note-taking API server.

There's no database or other "production ready" features. This tutorial is going to only focus on Elysia feature and how to use Elysia only.

We expected it to take around 15-20 minutes if you follow along.

Setup

Elysia is built on Bun, an alternative runtime to Node.js.

Install Bun if you haven't already.

MacOS/Linux

curl -fsSL https://bun.sh/install | bash

Windows

powershell -c "irm bun.sh/install.ps1 | iex"

Create a new project

# Create a new product
bun create elysia hi-elysia

# cd into the project
cd hi-elysia

# Install dependencies
bun install

This will create a barebone project with Elysia and basic TypeScript config.

Start the development server

bun dev

Open your browser and go to http://localhost:3000, you should see Hello Elysia message on the screen.

Elysia use Bun with --watch flag to automatically reload the server when you make changes.

Route

To add a new route, we specify an HTTP method, a pathname, and a value.

Let's start by opening the src/index.ts file as follows:

import { Elysia } from 'elysia'

const app = new Elysia()
    .get('/', () => 'Hello Elysia')
    .get('/hello', 'Do you miss me?') 
    .listen(3000)

Open http://localhost:3000/hello, you should see Do you miss me?.

There are several HTTP methods we can use, but we will use the following for this tutorial:

• get
• post
• put
• patch
• delete

Other methods are available, use the same syntax as get

import { Elysia } from 'elysia'

const app = new Elysia()
    .get('/', () => 'Hello Elysia')
    .get('/hello', 'Do you miss me?') 
    .post('/hello', 'Do you miss me?') 
    .listen(3000)

Elysia accept both value and function as a response.

However, we can use function to access Context (route and instance information).

import { Elysia } from 'elysia'

const app = new Elysia()
    .get('/', () => 'Hello Elysia') 
    .get('/', ({ path }) => path) 
    .post('/hello', 'Do you miss me?')
    .listen(3000)

Swagger

Entering a URL to the browser can only interact with the GET method. To interact with other methods, we need a REST Client like Postman or Insomnia.

Luckily, Elysia comes with a OpenAPI Schema with Scalar to interact with our API.

# Install the Swagger plugin
bun add @elysiajs/swagger

Then apply the plugin to the Elysia instance.

import { Elysia } from 'elysia'
import { swagger } from '@elysiajs/swagger'

const app = new Elysia()
    // Apply the swagger plugin
    .use(swagger()) 
    .get('/', ({ path }) => path)
    .post('/hello', 'Do you miss me?')
    .listen(3000)

Navigate to http://localhost:3000/swagger, you should see the documentation like this:

Now we can interact with all the routes we have created.

Scroll to /hello and click a blue Test Request button to show the form.

We can see the result by clicking the black Send button.

Decorate

However, for more complex data we may want to use class for complex data as it's allow us to define custom methods and properties.

Now, let's create a singleton class to store our notes.

import { Elysia } from 'elysia'
import { swagger } from '@elysiajs/swagger'

class Note { 
    constructor(public data: string[] = ['Moonhalo']) {} 
} 

const app = new Elysia()
    .use(swagger())
    .decorate('note', new Note()) 
    .get('/note', ({ note }) => note.data) 
    .listen(3000)

decorate allow us to inject a singleton class into the Elysia instance, allowing us to access it in the route handler.

Open http://localhost:3000/note, we should see ["Moonhalo"] on the screen.

For Scalar documentation, we may need to reload the page to see the new changes.

Path parameter

Now let's retrieve a note by its index.

We can define a path parameter by prefixing it with a colon.

import { Elysia } from 'elysia'
import { swagger } from '@elysiajs/swagger'

class Note {
    constructor(public data: string[] = ['Moonhalo']) {}
}

const app = new Elysia()
    .use(swagger())
    .decorate('note', new Note())
    .get('/note', ({ note }) => note.data)
    .get('/note/:index', ({ note, params: { index } }) => { 
        return note.data[index] 
Element implicitly has an 'any' type because index expression is not of type 'number'.
    }) 
    .listen(3000)

Let's ignore the error for now.

Open http://localhost:3000/note/0, we should see Moonhalo on the screen.

Path parameter allow us to retrieve a specific part from the URL. In our case, we retrieve a "0" from /note/0 put into a variable named index.

Validation

The error above is a warning that path parameter can be any string, while an array index should be a number.

For example, /note/0 is valid, but /note/zero is not.

We can enforce and validate type by declaring a schema:

import { Elysia, t } from 'elysia'
import { swagger } from '@elysiajs/swagger'

class Note {
    constructor(public data: string[] = ['Moonhalo']) {}
}

const app = new Elysia()
    .use(swagger())
    .decorate('note', new Note())
    .get('/note', ({ note }) => note.data)
    .get(
        '/note/:index',
        ({ note, params: { index } }) => {
            return note.data[index]
        },
        { 
            params: t.Object({ 
                index: t.Number() 
            }) 
        } 
    )
    .listen(3000)

We import t from Elysia to and define a schema for the path parameter.

Now, if we try to access http://localhost:3000/note/abc, we should see an error message.

This code resolve the error we have seen earlier because of TypeScript warning.

Elysia schema doesn't not only enforce validation on the runtime, but it also infers a TypeScript type for auto-completion and checking error ahead of time, and a Scalar documentation.

Most frameworks only provide only one of these features or provided them separately requiring us to update each one separately, but Elysia provides all of them as a Single Source of Truth.

Validation type

Elysia provide validation for the following properties:

• params - path parameter
• query - URL querystring
• body - request body
• headers - request headers
• cookie - cookie
• response - response body

All of them sharing the same syntax as the example above.

Status code

By default, Elysia will return a status code of 200 for all routes even if the response is an error.

For example, if we try to access http://localhost:3000/note/1, we should see undefined on the screen which shouldn't be a 200 status code (OK).

We can change the status code by returning an error

import { Elysia, t } from 'elysia'
import { swagger } from '@elysiajs/swagger'

class Note {
    constructor(public data: string[] = ['Moonhalo']) {}
}

const app = new Elysia()
    .use(swagger())
    .decorate('note', new Note())
    .get('/note', ({ note }) => note.data)
    .get(
        '/note/:index',
        ({ note, params: { index }, error }) => { 
            return note.data[index] ?? error(404) 
        },
        {
            params: t.Object({
                index: t.Number()
            })
        }
    )
    .listen(3000)

Now, if we try to access http://localhost:3000/note/1, we should see Not Found on the screen with a status code of 404.

We can also return a custom message by passing a string to the error function.

import { Elysia, t } from 'elysia'
import { swagger } from '@elysiajs/swagger'

class Note {
    constructor(public data: string[] = ['Moonhalo']) {}
}

const app = new Elysia()
    .use(swagger())
    .decorate('note', new Note())
    .get('/note', ({ note }) => note.data)
    .get(
        '/note/:index',
        ({ note, params: { index }, error }) => {
            return note.data[index] ?? error(404, 'oh no :(') 
        },
        {
            params: t.Object({
                index: t.Number()
            })
        }
    )
    .listen(3000)

Plugin

The main instance is starting to get crowded, we can move the route handler to a separate file and import it as a plugin.

Create a new file named note.ts:

note.ts

import { Elysia, t } from 'elysia'

class Note {
    constructor(public data: string[] = ['Moonhalo']) {}
}

export const note = new Elysia()
    .decorate('note', new Note())
    .get('/note', ({ note }) => note.data)
    .get(
        '/note/:index',
        ({ note, params: { index }, error }) => {
            return note.data[index] ?? error(404, 'oh no :(')
        },
        {
            params: t.Object({
                index: t.Number()
            })
        }
    )

Then on the index.ts, apply note into the main instance:

index.ts

import { Elysia, t } from 'elysia'
import { swagger } from '@elysiajs/swagger'

import { note } from './note'

class Note { 
    constructor(public data: string[] = ['Moonhalo']) {} 
} 

const app = new Elysia()
    .use(swagger())
    .use(note) 
    .decorate('note', new Note()) 
    .get('/note', ({ note }) => note.data) 
    .get(
        '/note/:index',
        ({ note, params: { index }, error }) => { 
            return note.data[index] ?? error(404, 'oh no :(') 
        },
        { 
            params: t.Object({ 
                index: t.Number() 
            }) 
        }
    ) 
    .listen(3000)

Open http://localhost:3000/note/1 and you should see oh no :( as same as before.

We have just created a note plugin, by declaring a new Elysia instance.

Each plugin is a separate instance of Elysia which has its own routes, middlewares, and decorators which can be applied to other instances.

Applying CRUD

We can apply the same pattern to create, update, and delete routes.

note.ts

import { Elysia, t } from 'elysia'

class Note {
    constructor(public data: string[] = ['Moonhalo']) {}

    add(note: string) { 
        this.data.push(note) 

        return this.data 
    } 

    remove(index: number) { 
        return this.data.splice(index, 1) 
    } 

    update(index: number, note: string) { 
        return (this.data[index] = note) 
    } 
}

export const note = new Elysia()
    .decorate('note', new Note())
    .get('/note', ({ note }) => note.data)
    .put('/note', ({ note, body: { data } }) => note.add(data), { 
        body: t.Object({ 
            data: t.String() 
        }) 
    }) 
    .get(
        '/note/:index',
        ({ note, params: { index }, error }) => {
            return note.data[index] ?? error(404, 'Not Found :(')
        },
        {
            params: t.Object({
                index: t.Number()
            })
        }
    )
    .delete( 
        '/note/:index', 
        ({ note, params: { index }, error }) => { 
            if (index in note.data) return note.remove(index) 

            return error(422) 
        }, 
        { 
            params: t.Object({ 
                index: t.Number() 
            }) 
        } 
    ) 
    .patch( 
        '/note/:index', 
        ({ note, params: { index }, body: { data }, error }) => { 
            if (index in note.data) return note.update(index, data) 

            return error(422) 
        }, 
        { 
            params: t.Object({ 
                index: t.Number() 
            }), 
            body: t.Object({ 
                data: t.String() 
            }) 
        } 
    ) 

Now let's open http://localhost:3000/swagger and try playing around with CRUD operation.

Group

If we look closely, all of the routes in note plugin all share a /note prefix.

We can simplify this by declaring prefix

note.ts

note.ts

export const note = new Elysia({ prefix: '/note' }) 
    .decorate('note', new Note())
    .get('/', ({ note }) => note.data) 
    .put('/', ({ note, body: { data } }) => note.add(data), {
        body: t.Object({
            data: t.String()
        })
    })
    .get(
        '/:index',
        ({ note, params: { index }, error }) => {
            return note.data[index] ?? error(404, 'Not Found :(')
        },
        {
            params: t.Object({
                index: t.Number()
            })
        }
    )
    .delete(
        '/:index',
        ({ note, params: { index }, error }) => {
            if (index in note.data) return note.remove(index)

            return error(422)
        },
        {
            params: t.Object({
                index: t.Number()
            })
        }
    )
    .patch(
        '/:index',
        ({ note, params: { index }, body: { data }, error }) => {
            if (index in note.data) return note.update(index, data)

            return error(422)
        },
        {
            params: t.Object({
                index: t.Number()
            }),
            body: t.Object({
                data: t.String()
            })
        }
    )

Guard

Now we may notice that there are several routes in plugin that has params validation.

We may define a guard to apply validation to routes in the plugin.

note.ts

export const note = new Elysia({ prefix: '/note' })
    .decorate('note', new Note())
    .get('/', ({ note }) => note.data)
    .put('/', ({ note, body: { data } }) => note.add(data), {
        body: t.Object({
            data: t.String()
        })
    })
    .guard({ 
        params: t.Object({ 
            index: t.Number() 
        }) 
    }) 
    .get(
        '/:index',
        ({ note, params: { index }, error }) => {
            return note.data[index] ?? error(404, 'Not Found :(')
        },
        { 
            params: t.Object({ 
                index: t.Number() 
            }) 
        } 
    )
    .delete(
        '/:index',
        ({ note, params: { index }, error }) => {
            if (index in note.data) return note.remove(index)

            return error(422)
        },
        { 
            params: t.Object({ 
                index: t.Number() 
            }) 
        } 
    )
    .patch(
        '/:index',
        ({ note, params: { index }, body: { data }, error }) => {
            if (index in note.data) return note.update(index, data)

            return error(422)
        },
        {
            params: t.Object({ 
                index: t.Number() 
            }), 
            body: t.Object({
                data: t.String()
            })
        }
    )

Validation will applied to all routes after guard is called and tie to the plugin.

Lifecycle

Now in real-world usage, we may want to do something like logging before the request is processed.

Instead of inline console.log for each route, we may apply lifecycle that intercept request before/after it is processed.

There are several lifecycle that we can use, but in this case we will be using onTransform.

note.ts

export const note = new Elysia({ prefix: '/note' })
    .decorate('note', new Note())
    .onTransform(function log({ body, params, path, request: { method } }) { 
        console.log(`${method} ${path}`, { 
            body, 
            params 
        }) 
    }) 
    .get('/', ({ note }) => note.data)
    .put('/', ({ note, body: { data } }) => note.add(data), {
        body: t.Object({
            data: t.String()
        })
    })
    .guard({
        params: t.Object({
            index: t.Number()
        })
    })
    .get('/:index', ({ note, params: { index }, error }) => {
        return note.data[index] ?? error(404, 'Not Found :(')
    })
    .delete('/:index', ({ note, params: { index }, error }) => {
        if (index in note.data) return note.remove(index)

        return error(422)
    })
    .patch(
        '/:index',
        ({ note, params: { index }, body: { data }, error }) => {
            if (index in note.data) return note.update(index, data)

            return error(422)
        },
        {
            body: t.Object({
                data: t.String()
            })
        }
    )

onTransform is called after routing but before validation, so we can do something like logging the request that is defined without 404 Not found route.

This allow us to log the request before it is processed, and we can see the request body and path parameters.

Scope

By default, lifecycle hook is encapsulated. Hook is applied to routes in the same instance, and is not applied to other plugins (routes that not defined in the same plugin).

This means onTransform log will not be called on other instance, unless we explicitly defined as scoped or global.

Authentication

Now we may want to add authorization to our routes, so only owner of the note can update or delete the note.

Let's create a user.ts file that will handle the user authentication:

import { Elysia, t } from 'elysia'

export const user = new Elysia({ prefix: '/user' })
    .state({
        user: {} as Record<string, string>,
        session: {} as Record<number, string>
    })
    .put(
        '/sign-up',
        async ({ body: { username, password }, store, error }) => {
            if (store.user[username])
                return error(400, {
                    success: false,
                    message: 'User already exists'
                })

            store.user[username] = await Bun.password.hash(password)

            return {
                success: true,
                message: 'User created'
            }
        },
        {
            body: t.Object({
                username: t.String({ minLength: 1 }),
                password: t.String({ minLength: 8 })
            })
        }
    )
    .post(
        '/sign-in',
        async ({
            store: { user, session },
            error,
            body: { username, password },
            cookie: { token }
        }) => {
            if (
                !user[username] ||
                !(await Bun.password.verify(password, user[username]))
            )
                return error(400, {
                    success: false,
                    message: 'Invalid username or password'
                })

            const key = crypto.getRandomValues(new Uint32Array(1))[0]
            session[key] = username
            token.value = key

            return {
                success: true,
                message: `Signed in as ${username}`
            }
        },
        {
            body: t.Object({
                username: t.String({ minLength: 1 }),
                password: t.String({ minLength: 8 })
            }),
            cookie: t.Cookie(
                {
                    token: t.Number()
                },
                {
                    secrets: 'seia'
                }
            )
        }
    )

Now there are a lot to unwrap here:

1. We create a new instance with 2 routes for sign up and sign in.
2. In the instance, we define an in-memory store user and session
   • 2.1 user will hold key-value of username and password
   • 2.2 session will hold a key-value of session and username
3. In /sign-in we insert a username and hashed password with argon2id
4. In /sign-up we does the following:
   • 4.1 We check if user exists and verify the password
   • 4.2 If the password matches, then we generate a new session into session
   • 4.3 We set cookie token with the value of session
   • 4.4 We append secret to cookie to add hash attacker from tampering with the cookie

TIP

As we are using an in-memory store, the data are wipe out every reload or every time we edit the code.

We will fix that in the later part of the tutorial.

Now if we want to check if user is signed in, we could check for value of token cookie and check with the `session store.

Reference Model

However, we can recognize that both /sign-in and /sign-up both share same body model.

Instead of copy-pasting the model all over the place, we could use a reference model to reuse the model by specifying a name.

To create a reference model, we may use .model and pass the name and the value of models:

import { Elysia, t } from 'elysia'

export const user = new Elysia({ prefix: '/user' })
    .state({
        user: {} as Record<string, string>,
        session: {} as Record<number, string>
    })
    .model({ 
    	signIn: t.Object({ 
    		username: t.String({ minLength: 1 }), 
    		password: t.String({ minLength: 8 }) 
    	}), 
     	session: t.Cookie( 
	     	{ 
	     		token: t.Number() 
	     	}, 
	     	{ 
		     	secrets: 'seia'
	     	} 
	    ) 
    }) 
    .model((model) => ({ 
    	...model, 
     	optionalSession: t.Optional(model.session) 
    })) 
    .put(
        '/sign-up',
        async ({ body: { username, password }, store, error }) => {
            if (store.user[username])
                return error(400, {
                    success: false,
                    message: 'User already exists'
                })
            store.user[username] = await Bun.password.hash(password)

            return {
                success: true,
                message: 'User created'
            }
        },
        {
           	body: 'signIn'
        }
    )
    .post(
        '/sign-in',
        async ({
            store: { user, session },
            error,
            body: { username, password },
            cookie: { token }
        }) => {
            if (
                !user[username] ||
                !(await Bun.password.verify(password, user[username]))
            )
                return error(400, {
                    success: false,
                    message: 'Invalid username or password'
                })

            const key = crypto.getRandomValues(new Uint32Array(1))[0]
            session[key] = username
            token.value = key

            return {
                success: true,
                message: `Signed in as ${username}`
            }
        },
        {
           	body: 'signIn', 
           	cookie: 'session', 
        }
    )

After adding a model/models, we can reuse them by referencing their name in the schema instead of providing a literal type while providing the same functionality and type safety.

We may also notice that, there's a remap model performing in this line:

import { Elysia } from 'elysia'

new Elysia()
	.model({
    	signIn: t.Object({
    		username: t.String({ minLength: 1 }),
    		password: t.String({ minLength: 8 })
    	}),
     	session: t.Cookie(
      		{
        		token: t.Number()
        	},
         	{
          		secrets: 'seia'
          	}
	   	)
    })
    .model((model) => ({ 
    	...model, 
     	optionalSession: t.Optional(model.session) 
    })) 

Elysia.model could accepts multiple overload:

1. Providing an object, the register all key-value as models
2. Providing a function, then access all previous models then return new models

By providing a function, we could do a remap/reference or filter out model we don't want to use.

However in our case we want to reference a model and create a new model from it. Notice that we create a new optionalSession model by referencing a model.session and wrap t.Optional over it.

The rest parameter ...rest is also important as we want to keep all the model while adding a new one.

Finally, we could add the /profile and /sign-out route as follows:

import { Elysia, t } from 'elysia'

export const user = new Elysia({ prefix: '/user' })
    .state({
        user: {} as Record<string, string>,
        session: {} as Record<number, string>
    })
    .model({
        signIn: t.Object({
            username: t.String({ minLength: 1 }),
            password: t.String({ minLength: 8 })
        }),
        session: t.Cookie(
            {
                token: t.Number()
            },
            {
                secrets: 'seia'
            }
        )
    })
    .model((model) => ({
        ...model,
        optionalSession: t.Optional(model.session)
    }))
    .put(
        '/sign-up',
        async ({ body: { username, password }, store, error }) => {
            if (store.user[username])
                return error(400, {
                    success: false,
                    message: 'User already exists'
                })

            store.user[username] = await Bun.password.hash(password)

            return {
                success: true,
                message: 'User created'
            }
        },
        {
            body: 'signIn'
        }
    )
    .post(
        '/sign-in',
        async ({
            store: { user, session },
            error,
            body: { username, password },
            cookie: { token }
        }) => {
            if (
                !user[username] ||
                !(await Bun.password.verify(password, user[username]))
            )
                return error(400, {
                    success: false,
                    message: 'Invalid username or password'
                })

            const key = crypto.getRandomValues(new Uint32Array(1))[0]
            session[key] = username
            token.value = key

            return {
                success: true,
                message: `Signed in as ${username}`
            }
        },
        {
            body: 'signIn',
            cookie: 'optionalSession'
        }
    )
    .get( 
        '/sign-out', 
        ({ cookie: { token } }) => { 
            token.remove() 

            return { 
                success: true, 
                message: 'Signed out'
            } 
        }, 
        { 
            cookie: 'optionalSession'
        } 
    ) 
    .get( 
        '/profile', 
        ({ cookie: { token }, store: { session }, error }) => { 
            const username = session[token.value] 

            if (!username) 
                return error(401, { 
                    success: false, 
                    message: 'Unauthorized'
                }) 

            return { 
                success: true, 
                username 
            } 
        }, 
        { 
            cookie: 'session'
        } 
    ) 

As we are going to apply authorization in the note, we are going to need to repeat 2 things:

1. Checking if user exists
2. Getting user id (in our case 'username')

For 1. instead of using guard, we could use a macro.

Plugin deduplication

As we are going to reuse this hook in multiple modules (user, and note), let's extract the service (utility) part out and apply to both modules.

import { Elysia, t } from 'elysia'

export const userService = new Elysia({ name: 'user/service' }) 
	.state({ 
        user: {} as Record<string, string>, 
        session: {} as Record<number, string> 
    }) 
    .model({ 
        signIn: t.Object({ 
            username: t.String({ minLength: 1 }), 
            password: t.String({ minLength: 8 }) 
        }), 
        session: t.Cookie( 
            { 
                token: t.Number() 
            }, 
            { 
                secrets: 'seia'
            } 
        ) 
    }) 
    .model((model) => ({ 
        ...model, 
        optionalSession: t.Optional(model.session) 
    })) 

export const user = new Elysia({ prefix: '/user' })
	.use(userService) 
	.state({ 
        user: {} as Record<string, string>, 
        session: {} as Record<number, string> 
    }) 
    .model({ 
        signIn: t.Object({ 
            username: t.String({ minLength: 1 }), 
            password: t.String({ minLength: 8 }) 
        }), 
        session: t.Cookie( 
            { 
                token: t.Number() 
            }, 
            { 
                secrets: 'seia'
            } 
        ) 
    }) 
    .model((model) => ({ 
        ...model, 
        optionalSession: t.Optional(model.session) 
    })) 

The name property here is very important, as it's a unique identifier for the plugin to prevent duplicate instance (like a singleton).

If we were to define the instance without the plugin, hook/lifecycle and routes and going to be register every time the plugin is used.

Our intention is to apply this plugin (service) to multiple modules to provide utility function, this make deduplication very important as life-cycle shouldn't be register twice.

Macro

Macro allows us to define a custom hook with custom life-cycle management.

To define a macro, we could use .macro as the follows:

import { Elysia, t } from 'elysia'

export const userService = new Elysia({ name: 'user/service' })
    .state({
        user: {} as Record<string, string>,
        session: {} as Record<number, string>
    })
    .model({
        signIn: t.Object({
            username: t.String({ minLength: 1 }),
            password: t.String({ minLength: 8 })
        }),
        session: t.Cookie(
            {
                token: t.Number()
            },
            {
                secrets: 'seia'
            }
        )
    })
    .model((model) => ({
        ...model,
        optionalSession: t.Optional(model.session)
    }))
    .macro(({ onBeforeHandle }) => ({ 
        isSignIn(enabled: boolean) { 
            if (!enabled) return

            onBeforeHandle( 
                ({ error, cookie: { token }, store: { session } }) => { 
                    if (!token.value) 
                        return error(401, { 
                            success: false, 
                            message: 'Unauthorized'
                        }) 

                    const username = session[token.value as unknown as number] 

                    if (!username) 
                        return error(401, { 
                            success: false, 
                            message: 'Unauthorized'
                        }) 
                } 
            ) 
        } 
    })) 

We have just create a new macro name isSignIn that accept boolean value, if it was true, then we add a onBeforeHandle event that execute after validation but before the main handler, allowing us to extract authentication logic here.

To use the macro, simply specified isSignIn: true as follows:

    .get(
        '/profile',
        ({ cookie: { token }, store: { session }, error }) => {
            const username = session[token.value]

            if (!username) 
                return error(401, { 
                    success: false, 
                    message: 'Unauthorized'
                }) 

            return {
                success: true,
                username
            }
        },
        {
            isSignIn: true, 
            cookie: 'session'
        }
    )

As we specified isSignIn, we can extract the imperative checking part, and reuse the same logic on multiple routes without copy-pasting the same code all over again.

TIP

This may seems like a small code change to trade for a larger boilerplate, but as the server grow complex, the user-checking could also grows to be a very complex mechanism as well.

Resolve

Our last objective is to get the username (id) from token, we could use resolve to define a new property into context same as store but only execute per request.

Unlike decorate and store, resolve is defined at beforeHandle stage or the value will be available after validation.

This ensure that the property like cookie: 'session' is exists before creating a new property.

export const getUserId = new Elysia() 
    .use(userService) 
    .guard({ 
        cookie: 'session'
    }) 
    .resolve(({ store: { session }, cookie: { token } }) => ({ 
        username: session[token.value] 
    })) 

In this instance, we define a new property username by using resolve, allowing us to reduce the getting username logic into a property instead.

We don't define a name in this getUserId instance because we want guard and resolve to reapply into multiple instance.

TIP

Same as macro, resolve plays well if the logic for getting the property is complex and might not worth for a small operation like this. But since in the real-world we are going to need database-connection, caching, and queuing might make it fits the narrative.

Scope

Now if we try to apply the use the getUserId, we might notice that the property username and guard isn't applied.

export const getUserId = new Elysia()
    .use(userService)
    .guard({
       	isSignIn: true,
        cookie: 'session'
    })
    .resolve(({ store: { session }, cookie: { token } }) => ({
        username: session[token.value]
    }))

export const user = new Elysia({ prefix: '/user' })
	.use(getUserId)
	.get('/profile', ({ username }) => ({
Property 'username' does not exist on type '{ body: unknown; query: Record<string, string | undefined>; params: never; headers: Record<string, string | undefined>; cookie: Record<string, Cookie<string | undefined>>; ... 8 more ...; error: <const Code extends number | keyof StatusMap, const T = Code extends 100 | ... 58 more ... | 511 ? { ...; }[Code] : Code>(...'.
        success: true,
        username
    }))

This is because Elysia encapsulate lifecycle by default as mention lifecycle

This is intentional by design, as we don't want each module to have a side-effect to other modules. Having a side-effect can be very difficult to debug especially in a large codebase with multiple (Elysia) dependencies.

If we want lifecycle to applied to the parent, we can explicitly annotate that it could be applied to the parent by using either:

1. scoped - only apply to parent at 1-level above only and not above
2. global - apply to all parent

In our case, we want to use scoped as it will apply to the controller that use the service only.

To do this, we need to annotate that life-cycle as scoped:

export const getUserId = new Elysia()
    .use(userService)
    .guard({
    	as: 'scoped', 
    	isSignIn: true,
        cookie: 'session'
    })
    .resolve(
    	{ as: 'scoped' }, 
     	({ store: { session }, cookie: { token } }) => ({
        	username: session[token.value]
      	})
    )

export const user = new Elysia({ prefix: '/user' })
	.use(getUserId)
	.get('/profile', ({ username }) => ({
        success: true,
        username
    }))

Alternatively, if we have multiple scoped define, we could use as to cast multiple life-cycle instead.

export const getUserId = new Elysia()
    .use(userService)
    .guard({
    	as: 'scoped', 
    	isSignIn: true,
        cookie: 'session'
    })
    .resolve(
   		{ as: 'scoped' }, 
    	({ store: { session }, cookie: { token } }) => ({
    	   	username: session[token.value]
    	})
    )
    .as('plugin') 

export const user = new Elysia({ prefix: '/user' })
	.use(getUserId)
	.get('/profile', ({ username }) => ({
        success: true,
        username
    }))

Both achieve the same effect, the only difference is single or multiple cast.

TIP

Encapsulation happens in both runtime, and type-level. This allows us to catch the error ahead of time.

Lastly, we can reuse userService and getUserId to help with authorization in our note controller.

But first, don't forget to import the user in the index.ts file:

index.ts

import { Elysia, t } from 'elysia'
import { swagger } from '@elysiajs/swagger'

import { note } from './note'
import { user } from './user'

const app = new Elysia()
    .use(swagger())
    .use(user) 
    .use(note)
    .listen(3000)

Authorization

First, let's modify the Note to store the user who created the note.

But instead of defining the Memo type, we can define a memo schema and infer the type from it, allowing us to sync runtime and type-level.

import { Elysia, t } from 'elysia'

const memo = t.Object({ 
	data: t.String(), 
	author: t.String() 
}) 

type Memo = typeof memo.static 

class Note {
    constructor(public data: string[] = ['Moonhalo']) {} 
    constructor( 
		public data: Memo[] = [ 
			{ 
				data: 'Moonhalo', 
				author: 'saltyaom'
			} 
		] 
	) {} 

    add(note: string) { 
    add(note: Memo) { 
        this.data.push(note)

        return this.data
    }

    remove(index: number) {
        return this.data.splice(index, 1)
    }

    update(index: number, note: string) { 
        return (this.data[index] = note) 
    } 
    update(index: number, note: Partial<Memo>) { 
        return (this.data[index] = { ...this.data[index], ...note }) 
    } 
}

export const note = new Elysia({ prefix: '/note' })
    .decorate('note', new Note())
    .model({ 
    	memo: t.Omit(memo, ['author']) 
    }) 
    .onTransform(function log({ body, params, path, request: { method } }) {
        console.log(`${method} ${path}`, {
            body,
            params
        })
    })
    .get('/', ({ note }) => note.data)
    .put('/', ({ note, body: { data } }) => note.add(data), { 
        body: t.Object({ 
            data: t.String() 
        }), 
    }) 
    .put('/', ({ note, body: { data }, username }) =>
    	note.add({ data, author: username }),
     	{ 
     		body: 'memo'
      	}
    ) 
    .guard({
        params: t.Object({
            index: t.Number()
        })
    })
    .get(
        '/:index',
        ({ note, params: { index }, error }) => {
            return note.data[index] ?? error(404, 'Not Found :(')
        }
    )
    .delete(
        '/:index',
        ({ note, params: { index }, error }) => {
            if (index in note.data) return note.remove(index)

            return error(422)
        }
    )
    .patch(
        '/:index',
        ({ note, params: { index }, body: { data }, error }) => { 
            if (index in note.data) return note.update(index, data) 
        ({ note, params: { index }, body: { data }, error, username }) => { 
        	if (index in note.data) 
         		return note.update(index, { data, author: username })) 

            return error(422)
        },
        {
            body: t.Object({ 
                data: t.String() 
            }), 
            body: 'memo'
        }
    )

Now let's import, and apply userService, getUserId to apply authorization to the note controller.

import { Elysia, t } from 'elysia'
import { getUserId, userService } from './user'

const memo = t.Object({
	data: t.String(),
	author: t.String()
})

type Memo = typeof memo.static

class Note {
    constructor(
		public data: Memo[] = [
			{
				data: 'Moonhalo',
				author: 'saltyaom'
			}
		]
	) {}

    add(note: Memo) {
        this.data.push(note)

        return this.data
    }

    remove(index: number) {
        return this.data.splice(index, 1)
    }

    update(index: number, note: Partial<Memo>) {
        return (this.data[index] = { ...this.data[index], ...note })
    }
}

export const note = new Elysia({ prefix: '/note' })
	.use(userService) 
    .decorate('note', new Note())
    .model({
        memo: t.Omit(memo, ['author'])
    })
    .onTransform(function log({ body, params, path, request: { method } }) {
        console.log(`${method} ${path}`, {
            body,
            params
        })
    })
    .get('/', ({ note }) => note.data)
    .use(getUserId) 
    .put(
        '/',
        ({ note, body: { data }, username }) =>
            note.add({ data, author: username }),
        {
            body: 'memo'
        }
    )
    .get(
        '/:index',
        ({ note, params: { index }, error }) => {
            return note.data[index] ?? error(404, 'Not Found :(')
        },
        {
            params: t.Object({
                index: t.Number()
            })
        }
    )
    .guard({
        params: t.Object({
            index: t.Number()
        })
    })
    .delete('/:index', ({ note, params: { index }, error }) => {
        if (index in note.data) return note.remove(index)

        return error(422)
    })
    .patch(
        '/:index',
        ({ note, params: { index }, body: { data }, error, username }) => {
            if (index in note.data)
                return note.update(index, { data, author: username })

            return error(422)
        },
        {
            isSignIn: true,
            body: 'memo'
        }
    )

And that's it 🎉

We have just implemented authorization by reusing the service we created earlier.

Error handling

One of the most important aspect of API is to make sure nothing goes wrong, and if it does, we need to handle it properly.

We use use onError lifecycle to catch any error that is thrown in the server.

index.ts

import { Elysia, t } from 'elysia'
import { swagger } from '@elysiajs/swagger'

import { note } from './note'
import { user } from './user'

const app = new Elysia()
    .use(swagger())
    .onError(({ error, code }) => { 
        if (code === 'NOT_FOUND') return

        console.error(error) 
    }) 
    .use(user)
    .use(note)
    .listen(3000)

We have just added an error listener that will catch any error that is thrown in the server, excluding 404 Not Found and log it to the console.

TIP

Notice that onError is at before use(note). This is important as Elysia apply method from top-to-bottom. The listener have to be applied before route.

And as onError is applied on the root instance, it doesn't need to define a scope as it will apply to all children instances.

Returning a truthy value will override a default error response, so we can return a custom error response while inherits the status code.

index.ts

import { Elysia, t } from 'elysia'
import { swagger } from '@elysiajs/swagger'

import { note } from './note'

const app = new Elysia()
    .use(swagger())
    .onError(({ error, code }) => { 
        if (code === 'NOT_FOUND') return 'Not Found :('

        console.error(error) 
    }) 
    .use(note)
    .listen(3000)

Observability

Now we have a working API, a final touch is to make sure everything is working after we deployed our server.

Elysia support OpenTelemetry by default with @elysiajs/opentelemetry plugin.

bun add @elysiajs/opentelemetry

Make sure to have a OpenTelemetry collector running otherwise we will be using Jaeger using docker.

docker run --name jaeger \
  -e COLLECTOR_ZIPKIN_HOST_PORT=:9411 \
  -e COLLECTOR_OTLP_ENABLED=true \
  -p 6831:6831/udp \
  -p 6832:6832/udp \
  -p 5778:5778 \
  -p 16686:16686 \
  -p 4317:4317 \
  -p 4318:4318 \
  -p 14250:14250 \
  -p 14268:14268 \
  -p 14269:14269 \
  -p 9411:9411 \
  jaegertracing/all-in-one:latest

Now let's apply OpenTelemetry plugin to our server.

index.ts

import { Elysia, t } from 'elysia'
import { opentelemetry } from '@elysiajs/opentelemetry'
import { swagger } from '@elysiajs/swagger'

import { note } from './note'
import { user } from './user'

const app = new Elysia()
    .use(opentelemetry()) 
    .use(swagger())
    .onError(({ error, code }) => {
        if (code === 'NOT_FOUND') return 'Not Found :('

        console.error(error)
    })
    .use(note)
    .use(user)
    .listen(3000)

Now try out some more requests and open http://localhost:16686 to see traces.

Select service Elysia and click on Find Traces, we should able to see list of requests that we have made.

Click on any of the request to see how long each lifecycle hook takes to process the request.

Click on the root parent span to see the request details, this will show you the request and response payload, and error if have any.

Elysia support OpenTelemetry out of the box, it automatically integrate with other JavaScript library that support OpenTelemetry like Prisma, GraphQL Yoga, Effect, etc.

You can also use other OpenTelemetry plugins to send traces to other services like Zipkin, Prometheus, etc.

Codebase recap

If you are following along, you should have a codebase that looks like this:

index.ts

import { Elysia } from 'elysia'
import { swagger } from '@elysiajs/swagger'
import { opentelemetry } from '@elysiajs/opentelemetry'

import { note } from './note'
import { user } from './user'

const app = new Elysia()
    .use(opentelemetry())
    .use(swagger())
    .onError(({ error, code }) => {
        if (code === 'NOT_FOUND') return 'Not Found :('

        console.error(error)
    })
    .use(user)
    .use(note)
    .listen(3000)

user.ts

import { Elysia, t } from 'elysia'

export const userService = new Elysia({ name: 'user/service' })
    .state({
        user: {} as Record<string, string>,
        session: {} as Record<number, string>
    })
    .model({
        signIn: t.Object({
            username: t.String({ minLength: 1 }),
            password: t.String({ minLength: 8 })
        }),
        session: t.Cookie(
            {
                token: t.Number()
            },
            {
                secrets: 'seia'
            }
        )
    })
    .model((model) => ({
        ...model,
        optionalSession: t.Optional(model.session)
    }))
    .macro(({ onBeforeHandle }) => ({
        isSignIn(enabled: boolean) {
            if (!enabled) return

            onBeforeHandle(
                ({ error, cookie: { token }, store: { session } }) => {
                    if (!token.value)
                        return error(401, {
                            success: false,
                            message: 'Unauthorized'
                        })

                    const username = session[token.value as unknown as number]

                    if (!username)
                        return error(401, {
                            success: false,
                            message: 'Unauthorized'
                        })
                }
            )
        }
    }))

export const getUserId = new Elysia()
    .use(userService)
    .guard({
    	isSignIn: true,
        cookie: 'session'
    })
    .resolve(({ store: { session }, cookie: { token } }) => ({
        username: session[token.value]
    }))
    .as('plugin')

export const user = new Elysia({ prefix: '/user' })
    .use(userService)
    .put(
        '/sign-up',
        async ({ body: { username, password }, store, error }) => {
            if (store.user[username])
                return error(400, {
                    success: false,
                    message: 'User already exists'
                })

            store.user[username] = await Bun.password.hash(password)

            return {
                success: true,
                message: 'User created'
            }
        },
        {
            body: 'signIn'
        }
    )
    .post(
        '/sign-in',
        async ({
            store: { user, session },
            error,
            body: { username, password },
            cookie: { token }
        }) => {
            if (
                !user[username] ||
                !(await Bun.password.verify(password, user[username]))
            )
                return error(400, {
                    success: false,
                    message: 'Invalid username or password'
                })

            const key = crypto.getRandomValues(new Uint32Array(1))[0]
            session[key] = username
            token.value = key

            return {
                success: true,
                message: `Signed in as ${username}`
            }
        },
        {
            body: 'signIn',
            cookie: 'optionalSession'
        }
    )
    .get(
        '/sign-out',
        ({ cookie: { token } }) => {
            token.remove()

            return {
                success: true,
                message: 'Signed out'
            }
        },
        {
            cookie: 'optionalSession'
        }
    )
    .use(getUserId)
    .get('/profile', ({ username }) => ({
        success: true,
        username
    }))

note.ts

import { Elysia, t } from 'elysia'
import { getUserId, userService } from './user'

const memo = t.Object({
    data: t.String(),
    author: t.String()
})

type Memo = typeof memo.static

class Note {
    constructor(
        public data: Memo[] = [
            {
                data: 'Moonhalo',
                author: 'saltyaom'
            }
        ]
    ) {}

    add(note: Memo) {
        this.data.push(note)

        return this.data
    }

    remove(index: number) {
        return this.data.splice(index, 1)
    }

    update(index: number, note: Partial<Memo>) {
        return (this.data[index] = { ...this.data[index], ...note })
    }
}

export const note = new Elysia({ prefix: '/note' })
    .use(userService)
    .decorate('note', new Note())
    .model({
        memo: t.Omit(memo, ['author'])
    })
    .onTransform(function log({ body, params, path, request: { method } }) {
        console.log(`${method} ${path}`, {
            body,
            params
        })
    })
    .get('/', ({ note }) => note.data)
    .use(getUserId)
    .put(
        '/',
        ({ note, body: { data }, username }) =>
            note.add({ data, author: username }),
        {
            body: 'memo'
        }
    )
    .get(
        '/:index',
        ({ note, params: { index }, error }) => {
            return note.data[index] ?? error(404, 'Not Found :(')
        },
        {
            params: t.Object({
                index: t.Number()
            })
        }
    )
    .guard({
        params: t.Object({
            index: t.Number()
        })
    })
    .delete('/:index', ({ note, params: { index }, error }) => {
        if (index in note.data) return note.remove(index)

        return error(422)
    })
    .patch(
        '/:index',
        ({ note, params: { index }, body: { data }, error, username }) => {
            if (index in note.data)
                return note.update(index, { data, author: username })

            return error(422)
        },
        {
            isSignIn: true,
            body: 'memo'
        }
    )

Build for production

Finally we can bundle our server into a binary for production using bun build:

bun build \
	--compile \
	--minify-whitespace \
	--minify-syntax \
	--target bun \
	--outfile server \
	./src/index.ts

This command is a bit long, so let's break it down:

1. --compile - Compile TypeScript to binary
2. --minify-whitespace - Remove unnecessary whitespace
3. --minify-syntax - Minify JavaScript syntax to reduce file size
4. --target bun - Target the bun platform, this can optimize the binary for the target platform
5. --outfile server - Output the binary as server
6. ./src/index.ts - The entry file of our server (codebase)

Now we can run the binary using ./server and it will start the server on port 3000 same as using bun dev.

./server

Open your browser and navigate to http://localhost:3000/swagger, you should see the same result as using dev command.

By minifying the binary not only that we made our server small and portable, but it also significantly reduce memory usage.

TIP

Bun does have --minify flag that will minify the binary, however it include --minify-identifiers, and as we are using OpenTelemetry, it's going to rename function name and make tracing harder than it should.

WARNING

Exercise: Try run development server and production server, and compare the memory usage.

Development server will use a process name 'bun', while production server will use the name 'server'.

Wrapping up

And- that's it 🎉

We have created a simple API using Elysia, we have learned how to create a simple API, how to handle errors, and how to observe our server using OpenTelemetry.

You could to take a step further by trying to connect to a real database, connect to a real frontend or implement a real-time communication with WebSocket.

This Tutorial cover most of the concept we need to know to create Elysia server, however there are some several useful concepts you might want to know.

If you are stuck

Feels free to ask our community on GitHub Discussions, Discord, and Twitter, if you have any further question.

We wish you happy on your journey with Elysia ❤️