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A tiny, simple dependency injection framework for dummies.

Goals:

• Define your dependencies in a file
• Support robust dependency mocking

Anti-goals:

• Decorators
• Forcing your code to use classes
• Automatic memoization
• Graph algorithms

Examples:

The simplest possible dependency registry is just an object:

import { registry } from "antipattern";
export const deps = registry({
  hello() {
    return "world";
  },
});

// elsewhere:
registry.hello(); // returns "world"

// mocking with automatic restoration:
await withMock(registry, "hello", () => "moon", async () => {
  registry.hello(); // returns "moon"
});

registry.hello(); // returns "world" again

To express dependency graphs, just use this, like with regular JS:

import { registry } from "antipattern";
export const deps = registry({
  hello() {
    return `hello ${this.subject()}`;
  },
  subject() {
    return "world";
  },
});

// elsewhere:
await withMock(registry, "subject", () => "alligator", async () => {
  expect(registry.hello()).toBe("hello alligator");
});

Remember that with this, you have to define your object's functions like this:

{
  method() {
    // you can call `this` in here, and it refers to the object
  },
}

And not like this:

{
  method: () => {
    // Arrow functions will bind `this` to the outer-level `this` scope, and not
    // to the object, so you can't call the object's own functions with `this`
  },
}

If you don't want to expose everything to callers, but you still want the internal functions to call the mockable methods, the registry function can also take a class, allowing you to define private fields or methods:

import { registry } from "antipattern";
import { memo } from "radash";

export const deps = registry(class {
  user() {
    return process.env.USER;
  }
  pass() {
    return process.env.PASS;
  }
  login() {
    return `${this.user()}:${this.pass()}`;
  }
  cloud() {
    if(process.env.NODE_ENV === "development") return this.local();
    return this.aws();
  }

  private aws() {
    // you can call this.user() in here, despite not exposing .aws publically,
    // and it'll use the mocked value if it's been mocked
  }

  private local() {
    // ditto
  }
});

// elsewhere:
const cloud = await deps.cloud();
await cloud.upload("./README.md");

You can also manually set and unset mocks using the plain mock function, which returns a restore function that will restore the original value:

import { mock } from "antipattern";

beforeEach(() => {
  const restores: Array<() => any> = [];
  restores.push(mock(deps, "user", () => "reissbaker"));
  restores.push(mock(deps, "pass", () => "hunter2s"));
  return () => {
    restores.forEach(restore => restore());
  };
});