eventable.js

'use strict';

/** Base class for generic event handling.
 * @example
 *
 * // Don’t forget to call `super()` if defining a constructor.
 * class Foo extends Eventable {}
 * let foo = new Foo();
 *
 * foo.on('bar', (data) => console.log(data));
 * // will log “Hello world!”
 * foo.trigger('bar', 'Hello World!');
 * foo.off('bar');
 *
 * // Namespaced events:
 * * foo.on('bar.mynamespace', (data) => console.log(data));
 * // will log “Hello world!”
 * foo.trigger('bar', 'Hello World!');
 * // will remove all events in namespace
 * foo.off('.mynamespace');
 */
class Eventable {

  /**
   * Create an eventable instance.
   * @constructor
   */
  constructor() {
    this.listeners = {};
  }


  /**
   * Register an event.
   * @param {string} event - The name of the event. May be namespaced.
   * @param {function} callback - Callback function.
   */
  on(event, callback) {
    this.listeners[event] = this.listeners[event] || [];
    this.listeners[event].push(callback);
  }


  /**
   * Unregister an event.
   * @param {string} event - The name of the event or namespace to unregister.
   * @param {function} [callback] - Callback function to unregister.
   */
  off(event, callback) {
    // Remove all handlers
    if (event === undefined) {
      // This should be a map but JS doesn’t provide any simple facilitiy
      // to filter by keys (use case: namespace) hence we’ll resort to using
      // an object instead.
      this.listeners = {};
      return true;
    }

    // Remove all events in namespace
    if (event.startsWith('.')) {
      let listeners = {};

      // Filter out listeners for namespace
      for (let key of Object.keys(this.listeners)) {
        if (key.split('.')[1] !== event.replace(/^./, '')) {
          listeners[key] = this.listeners[key];
        }
      }
      this.listeners = listeners;

    } else {
      let handlers = this.listeners[event];

      // No handlers found or defined, do nothing
      if (!handlers || !handlers.length) return false;

      if (callback) {
        this.listeners[event] = handlers.filter((handler) => {
          return typeof handler == 'function' && handler !== callback;
        });
      } else {
        this.listeners[event] = [];
      }
    }

    return true;
  }


  /**
   * Trigger an event.
   * @param {string} event - The name of the event.
   * @arg {...*} [args] - Data to be passed to callback.
   */
  trigger(event, ...args) {
    let listeners = [];
    for (let key of Object.keys(this.listeners)) {
      if (key === event || key.split('.')[0] === event) {
        listeners = listeners.concat(this.listeners[key]);
      }
    }

    if (listeners && listeners.length) {
      listeners.forEach((listener) => listener(...args));
      return true;
    }
    return false;
  }

}

module.exports = Eventable;

eventable_spec.js

let assert = require('assert');
let sinon = require('sinon');

let Eventable = require('../eventable');

class Foo extends Eventable {}

describe('Eventable', function() {
  let foo, spy;

  beforeEach(function() {
    foo = new Foo();
    spy = new sinon.spy();
  })

  describe('#on()', function() {
    it('should register callback for event', function() {
      foo.on('bar', spy);
      foo.trigger('bar');
      assert(spy.called);
    });
  });

  describe('#off()', function() {
    it('should unregister a handler for event', function() {
      foo.on('bar', spy);
      foo.off('bar');
      foo.trigger('bar');
      assert(spy.notCalled);
    });

    it('should unregister only a certain handler for an event', function() {
      let otherSpy = new sinon.spy();
      foo.on('bar', spy);
      foo.on('bar', otherSpy);
      foo.off('bar', spy);
      foo.trigger('bar');
      assert(spy.notCalled);
      assert(otherSpy.called);
    });

    it('remove all events', function() {
      foo.on('bar', spy);
      foo.off();
      foo.trigger('bar');
      assert(spy.notCalled);
    });

    it('remove all events for namespace', function() {
      foo.on('bar.namespace', spy);
      foo.off('.namespace');
      foo.trigger('bar');
      assert(spy.notCalled);
    });

    it('doesn\'t remove events outside of namespace', function() {
      foo.on('bar.namespace', function() {});
      foo.on('bar', spy);
      foo.off('.namespace');
      foo.trigger('bar');
      assert(spy.called);
    });
  });

  describe('#trigger()', function() {
    it('should not trigger if no event is defined', function() {
      foo.on('other', spy);
      foo.trigger('bar');
      assert(spy.notCalled);
    });

    it('should not trigger other events', function() {
      let otherSpy = new sinon.spy();
      foo.on('bar', spy);
      foo.on('other', otherSpy);
      foo.trigger('bar');
      assert(spy.called);
      assert(otherSpy.notCalled);
    });

    it('should pass data to callback', function() {
      foo.on('bar', spy);
      foo.trigger('bar', 'baz');
      assert(spy.calledWith('baz'));
    });

    it('should trigger namespaced event', function() {
      foo.on('bar.namespace', spy);
      foo.trigger('bar.namespace');
      assert(spy.called);
    });

    it('should trigger namespaced event without namespace', function() {
      foo.on('bar.namespace', spy);
      foo.trigger('bar');
      assert(spy.called);
    });
  });

});

package.json

{
  "name": "eventable",
  "version": "1.0.0",
  "description": "Base class for event handling.",
  "main": "eventable.js",
  "scripts": {
    "test": "mocha eventable_spec.js"
  },
  "keywords": [
    "event",
    "handling"
  ],
  "author": "Florian Plank",
  "license": "MIT"
}

This doesn't get the attention it deserves. Now that we have decorators this is very useful. Thanks!

Thanks for your code, really helps me to implement a lib's event system!