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Dependency Injection

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Since version 2.0.0, dependency injection, thanks to iti, is a feature to customize your bot’s utilities and structures.

For example, a minimal setup for any project might look like this:

src/index.ts
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const client = new Client({
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  ...options,
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});
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Sern.makeDependencies<MyDependencies>({
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  build: (root) =>
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    root.add({
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      "@sern/client": single(() => client),
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    }),
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});

For any TypeScript project, you’ll need to add an interface to get intellisense and typings.

src/dependencies.d.ts
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interface MyDependencies extends Dependencies {
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  "@sern/client": Singleton<Client>;
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}

Full Example

Your full setup may have the following structure:

  • Directorysrc/
    • index.ts (your main file and client)
    • dependencies.d.ts (for intellisense)
src/index.ts
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const client = new Client({
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  ...options,
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});
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interface MyDependencies extends Dependencies {
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  "@sern/client": Singleton<Client>;
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}
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export const useContainer = Sern.makeDependencies<MyDependencies>({
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  build: (root) =>
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    root.add({
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      "@sern/client": single(() => client),
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    }),
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});

Everything else is handled. However, you may want customize things.

Adding Dependencies to Root

Each sern built dependency must implement its contracts:

  • @sern/logger: Logging data → Logging
  • @sern/errors: Handling errors and lifetime → ErrorHandling
  • @sern/modules: Managing all command modules → ModuleManager
  • @sern/emitter: The key to emit events and occurences in a project → Emitter

You may also add disposers so that when the application crashes, the targeted dependency calls that function.

src/index.ts
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export const useContainer = Sern.makeDependencies<MyDependencies>({
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  build: (root) =>
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    root
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      .add({
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        "@sern/client": single(() => client),
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      })
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      .addDisposer({ "@sern/client": (client) => client.destroy() }),
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});

Init

  1. Do you need to perform intializing behavor for a dependency?

    src/database.ts
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    import { Init } from "@sern/handler";
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    class Database implements Init {
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      init() {
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        await this.connect();
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        console.log("Connected");
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      }
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    }

  2. Modify your Dependencies interface:

    src/dependencies.d.ts
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    import type { Initializable } from "@sern/handler";
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    interface Dependencies extends CoreDependencies {
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      database: Initializable<Database>;
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    }

  3. Make sure its been added:

    src/index.ts
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    await makeDependencies({
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        build: root => root
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            .add({ database => new Database() })
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    })

  4. Now, when your bot starts, the init method will be called. 🎉