Elysia.js

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Dependency Injection ​

Sometimes you would like to separate routes from your main file.

Normally you would normally decouple them into a plugin like:

typescript
// index.ts
const app = new Elysia()
    .use(authenRoute)
    .use(profileRoute)
    // and so on...

// routes/authen.ts
const authen = (app: Elysia) => app
    .post('/sign-in', signIn)
    .post('/sign-up', signUp)

// index.ts
const app = new Elysia()
    .use(authenRoute)
    .use(profileRoute)
    // and so on...

// routes/authen.ts
const authen = (app: Elysia) => app
    .post('/sign-in', signIn)
    .post('/sign-up', signUp)

But then sometime, at the main instance introduce some state, and decorate that you might need a separated module.

typescript
// index.ts
const app = new Elysia()
    .decorate('signOut', signOut)
    .state('redis', redis)
    .use(authenRoute)
    .use(profileRoute)
    // and so on...

// routes/authen.ts
const authen = (app: Elysia) => app
    .post('/sign-in', signIn)
    .post('/sign-up', signUp)
    // But then there is no type
    .post('/sign-out', ({ signOut, store: { db } }) => {
        signOut()

        db.doSomething()
    })

// index.ts
const app = new Elysia()
    .decorate('signOut', signOut)
    .state('redis', redis)
    .use(authenRoute)
    .use(profileRoute)
    // and so on...

// routes/authen.ts
const authen = (app: Elysia) => app
    .post('/sign-in', signIn)
    .post('/sign-up', signUp)
    // But then there is no type
    .post('/sign-out', ({ signOut, store: { db } }) => {
        signOut()

        db.doSomething()
    })

If you hovered over the main app in index.ts, you can see that it has some type auto-generated for your main server which might look something like this:

typescript
const app: Elysia<{
    store: {
        redis: Redis;
     };
     request: {
        signOut: () => void;
     };
     schema: {};
}>

const app: Elysia<{
    store: {
        redis: Redis;
     };
     request: {
        signOut: () => void;
     };
     schema: {};
}>

But this type isn't applied to sub-modules.

To apply the type to sub-modules, you can create a plugin which only contains state and decorate which caused type side-effect as dependency, and apply to the module you want to use.

typescript
const setup = (app: Elysia) => app
    .decorate('signOut', signOut)
    .state('redis', redis)

// routes/authen.ts
const authen = (app: Elysia) => app
    .use(setup)
    .post('/sign-in', signIn)
    .post('/sign-up', signUp)
    // Now it's strictly typed
    .post('/sign-out', ({ signOut, store: { db } }) => {
        signOut()

        db.doSomething()
    })

const setup = (app: Elysia) => app
    .decorate('signOut', signOut)
    .state('redis', redis)

// routes/authen.ts
const authen = (app: Elysia) => app
    .use(setup)
    .post('/sign-in', signIn)
    .post('/sign-up', signUp)
    // Now it's strictly typed
    .post('/sign-out', ({ signOut, store: { db } }) => {
        signOut()

        db.doSomething()
    })

This will allows you to control access to decorators in modules, this concept is also known as Dependency Injection but only for types.