Dependency Injection Patterns

Dependency Injection Patterns

TL;DR

Every Webiny extension type uses the same DI pattern: define a class implementing *.Interface, declare dependencies in the constructor, and export via *.createImplementation({ implementation, dependencies }). The DI container automatically provides the required services, ensures type safety, and validates at compile time. This pattern is the connective tissue across all extension types -- API, Admin, CLI, and Infrastructure.

Working Context

This skill applies to both extension developers (working in extensions/) and core developers (working in packages/). The DI pattern is universal — only the import paths differ.

Detect which context you're in by checking the file path: extensions/ → extension mode, packages/ → core mode. The dependencies array, constructor injection, scoping rules, and all other patterns are identical in both contexts.

The Universal Pattern

import { SomeFactory } from "webiny/some/path";
import { Logger, BuildParams } from "webiny/api";

class MyImplementation implements SomeFactory.Interface {
  constructor(
    private logger: Logger.Interface,
    private buildParams: BuildParams.Interface
  ) {}

  execute(/* factory-specific params */) {
    this.logger.info("Doing something...");
    // buildParams.get() returns T | null — always account for null.
    const value = this.buildParams.get<string>("MY_PARAM");
  }
}

export default SomeFactory.createImplementation({
  implementation: MyImplementation,