Jimmy

This is a simple library for using the mediator pattern in your typescript and deno projects. While not entirely a true port, the MediatR library for .NET is a direct influence.

Why Jimmy?

1. Former US President Jimmy Carter was known for his ability at being a great mediator.
2. The .NET Core library MediatR was written by Jimmy Bogard.
3. Coicdence? I think not.

Installation

Node.js

# npm
npm install --save @myty/jimmy
npx jsr add @myty/jimmy

Deno

import { Mediator, Request, Notification } from "jsr:@myty/jimmy";

Usage

const mediator = new Mediator();

class TestRequest extends Request<Promise<string>> {
  constructor(public name: string) {
    super();
  }
}

mediator.handle(
  TestRequest,
  (request) => Promise.resolve(`Hello, ${request.name}!`),
);

const response = await mediator.send(new TestRequest("Jimmy"));

console.log(response); // "Hello, Jimmy!"

Progress

Jimmy is inspired by the MediatR project, so here's what's been implemented:

• Request/Response messages
• Notification messages
• Publish Strategies (Notifications)

Basics

Just like MediatR, Jimmy has two kinds of messages it dispatches:

• Request/response messages, dispatched to a single handler
• Notification messages, dispatched to multiple handlers

Request/Response

The request/response interface handles both command and query scenarios. First, create a message:

class Ping extends Request<Promise<string>> {}

Next, register a handler:

mediator.handle(Ping, (request) => Promise.resolve("Pong"));

Finally, send a message through the mediator:

const response = await mediator.send(new Ping());
console.log(response); // "Pong"

In the case your message does not require a response, use Request<Promise<void>> as your base class :

class OneWay extends Request<Promise<void>> {}
mediator.handle(OneWay, () => {
  // Twiddle thumbs
  Promise.resolve();
});

Or if the request is completely synchronous, inherit from the base Request class without any generic parameters. void is the default return type.

class Ping extends Request {}
mediator.handle(Ping, () => "Pong");

Notifications

For notifications, first create your notification message:

class Ping extends Notification {}

Next, register zero or more handlers for your notification:

mediator.handle(Ping, (notification) => {
   console.log("Pong 1");
   return Promsie.resolve();
}

mediator.handle(Ping, (notification) => {
   console.log("Pong 2");
   return Promsie.resolve();
}

Finally, publish your message via the mediator:

await mediator.publish(new Ping());

Publish Strategies

The default implementation of Publish loops through the notification handlers and awaits each one. This ensures each handler is run after one another.

Depending on your use-case for publishing notifications, you might need a different strategy for handling the notifications. Maybe you want to publish all notifications in parallel, or wrap each notification handler with your own exception handling logic.