Simple Event Bus

This project implements a basic but configurable event bus.

Usage

// In Node.js
const EventBus = require('simple-event-bus');
 
// For the browser, using a bundler
import EventBus from 'simple-event-bus';
 
const eventBus = new EventBus();
 
// subscribe to events
const removeHandler = eventBus.on('my-event', (...args) => {
  console.log(...args);
});
 
// trigger events
eventBus.emit('my-event', 'Hello', 'world', '!');
// => Hello world !
 
// unsubscribe when you are done
removeHandler();

Live Demo and its source code.

Features

• An error in one of the handlers will not stop the propagation of the event to other handlers.
• Simple api: adding a handler returns the function to remove it.
• Handlers are called in the order of insertion.
• Customizable logger (to plug your custom logging logic).
• Customizable broker (to transform messages between events emitted and handlers).

API

new EventBus([options: Object])

Returns the event bus instance, that holds the handlers and is able to dispatch events

eventBus.on(action: string, handler: Function, [handlerId: number]): Function

Registers the handler for the given action. Optionally, a handlerId can be passed, that will be used when logging errors. It returns a function that removes the handler when called.

eventBus.emit(action: string, ...parameters: any): number

Emits an event, dispatching it to all registered handlers. It does not do anything if no handlers have been registered on that event.

eventBus.handlersCount(action: string)

Returns the number of handlers currently subscribed to the action.

[options = {}]

options.logger

Type: Object Default: console

The only mandatory method for now is error, but some additional loggings will most likely be added (log, info, debug, warn);

options.broker

Type: Function Default: (action, ...payload) => payload

A function to customize the interface between events and handlers, giving the ability for example to standardize all the messages transmitted to the handlers into a normalized format. By default, the broker just propagates the arguments that have been emitted.

Compatibility

The node entry point ("main": "index.js" in the package.json) requires Node >= 6.5 (see ES6 compatibility table for class). The browser entry point ("browser": "browser.js" in the package.json) exposes some code bundled and transpiled into ES5 for compatibility with older browsers, bundlers, minifiers, ...

Future

• More logging: Currently, we only log errors. We could log more information, to help with troubleshooting.

• Log level: We could add a logLevel option, to allow filtering the log messages while still keeping the default logger.

• Test framework: A better test framework (for example Jest) should be used in order to for example have a test coverage report.

• Examples: A showcase application could be built as a demo, showing the interest of using a custom logger and broker in a real-case example.