NodeJS Event Manager

A NodeJS Event Manager using builtin NodeJS Events.

The main purpose of this package, is to facilitate the use of events, in a node JS application.

It implements the same "api" ("interface") as rabbitmq-event-manager so you can easily switch from NodeJS to RabbitMQ of vice-versa.

It can be usefull for testing purpose, but also in order to start quickly with nodeJS and if your application is getting bigger and you want to externalize some parts, you can deploy a RabittMQ and make your applications communicate together

Install

npm install nodejs-event-manager

Or with Yarn

yarn add nodejs-event-manager

Basic Example

• Initialize

import EventManager from "nodejs-event-manager";
const myEventManager = new EventManager();
myEventManager
  .initialize()
  .then(() => {
    /** Do something after initialization */
  })
  .catch(err => {
    /** An error occured while initialization */
  });

• Consumer

import EventManager from 'nodejs-event-manager';
const myEventManager = new EventManager({appName:'CONSUMER');
myEventManager.on('MY_EVENT_NAME', async (payload)=>{
    console.log(payload);
});

• Producer

import EventManager from "nodejs-event-manager";
const myEventManager = new EventManager({ appName: "PRODUCER_1" });
 
myEventManager.emit("MY_EVENT_NAME", payload);

NOTE: ⚠️ A very good convention may be to prefix the name of the event with the emitter application name, for example : PRODUCER_1.MY_EVENT_NAME but it's not mandatory.

Then we can create new Consumer and listen the same event :

import EventManager from 'nodejs-event-manager';
const myEventManager = new EventManager({appName:'OTHER_CONSUMER');
myEventManager.on('MY_EVENT_NAME', async (payload)=>{
    console.log(payload);
});

Options

Name	Type	Default	Description
appName	String	-	The name of the application (used for naming exchanges and queues).
metas	boolean or (function)	true	Weither or not to add _metas infirmations in the event, If a function this returned value, will become the _metas object (see )
logPrefix	string	[RABBITMQ]	The text that will be printed before the error log
logLevel	string	error	The log Level (see winston logLevels)
logTransportMode	string	console	Mute (no log), or output to console. Possible values are ("console" or "mute")
defaultResponseSuffix	string	'.RESPONSE'	The suffix to add to the response event name.
emitAndWaitTimeout	number	30000	the timeout when emit and wait

Metas Informations

By defaut, some metas data are added to the payload :

• guid : A unique id generated, to be able to debug for example, or for following the event.
• timestamp : A number of milliseconds elapsed since January 1, 1970 00:00:00 UTC. (Date.now())
• name : A string which is the name of the emitted event.
• applicationName: The value of the application which emits the Event.

So if your payload is :

{
  userId: 42;
}

With Metas data it will be :

{
    _metas:{
        guid: '465e008c-d37f-4e31-b494-023e6d187946',
        name: 'MY_EVENT_NAME',
        timestamp: 1519211809934,
        applicationName: 'PRODUCER_1'
    },
    userId:42
}

You can remove metas informations by settings the option value "metas" to false.

You can also override the metas generation by giving a function as metas options value (on the emitter side only, as the event is generated there).

With no metas

import EventManager from "rabbitmq-event-manager";
const myEventManagerWithNoMetas = new EventManager({
  url: "amqp://localhost",
  appName: "PRODUCER_1",
  metas: false
});
const payload = { userId: 42 };
myEventManagerWithNoMetas.emit("MY_EVENT_NAME", payload);
// Payload will be
// {
//    userId:42
// }

Override Metas

import EventManager from "rabbitmq-event-manager";
const myEventManagerOverrideMetas = new EventManager({
  url: "amqp://localhost",
  appName: "PRODUCER_1",
  metas: sourceMetas => {
    // sourceMetas contains the default metaa
    return {
      ...sourceMetas,
      otherProperty: "MyValue"
    };
  }
});
const payload = { userId: 42 };
myEventManagerOverrideMetas.emit("MY_EVENT_NAME", payload);
// Payload will be
// {
//    _metas: {
//        guid : '465e008c-d37f-4e31-b494-023e6d187947'
//        name: 'MY_EVENT_NAME',
//        timestamp: 1519211809934,
//        otherProperty:'MyValue'
//    }
//    userId:42
// }

Emit and wait

• since version 1.1.0 An example with a test :

it("Should be able to emit and wait for response two times", async () => {
  /** given */
 
  /** when */
  eventManager.on("add", async payload => {
    return { result: payload.a + payload.b };
  });
 
  await pause(500);
  const add1 = await eventManager.emitAndWait("add", { a: 3, b: 42 });
  const add2 = await eventManager.emitAndWait("add", { a: 3, b: 3 });
  await pause(500);
  /** then */
  expect(add1.result).to.equal(45);
  expect(add2.result).to.equal(6);
});