typed-event-emitter

typed-event-emitter

This module provides an alternative API than the well known event emitting interfaces used in the browser (DOM) or node.js. Instead of accepting arbitrary strings as the event name, this module forces you to register your events in your class. Consequently, the style of binding and emitting events differs a little bit, ensuring already at binding time that the events actually exists.

Install

Via npm:

$ npm install typed-event-emitter

Usage

Take a look at the following snippet (TypeScript):

import { EventEmitter } from 'typed-event-emitter';

class MyClass extends EventEmitter {
  public readonly onValueChanged = this.registerEvent<[number]>();
  
  private _value: number;
  
  constructor(value: number) {
    // initialize EventEmitter
    super();
    
    this._value = value;
  }
  
  get value() {
    return this._value;
  }
  
  set value(value: number) {
    this._value = value;
    this.emit(this.onValueChanged, this._value);
  }
}

let instance = new MyClass(0);
instance.onValueChanged(newValue => {
  console.log(`Value changed: ${newValue}`);
});

instance.value = 27;

First, the EventEmitter is loaded from the module. Any class that shall emit events must extend that EventEmitter. If your class has its own constructor, make sure to call super().

Any events your class shall be able to emit must be registered in the form:

onFooBar = this.registerEvent<callbackArgTypes>();

Where onFooBar can be any name (it doesn't need to begin with on) and callbackArgTypes must be an array of the argument types the callback accepts. With this, you can see the signature your function must have when you're about to bind a listener to that event.

To fire/emit an event (only possible from within your event emitter), you have to call this.emit(this.onFooBar, ...), where this.onFooBar is the event to emit and ... any number of parameters that will be passed to the listeners.

JavaScript

The code shown above can also be written in JavaScript (node.js):

const EventEmitter = require('typed-event-emitter').EventEmitter;

class MyClass extends EventEmitter {
  constructor(value) {
    // initialize EventEmitter
    super();
    
    /* newValue: number */
    this.onValueChanged = this.registerEvent();
    
    this._value = value;
  }
  
  get value() {
    return this._value;
  }
  
  set value(value) {
    this._value = value;
    this.emit(this.onValueChanged, this._value);
  }
}
 
let instance = new MyClass(0);
instance.onValueChanged(newValue => {
  console.log(`Value changed: ${newValue}`);
});
 
instance.value = 27;

Note that the events are registered explicitly within the constructor. Make sure to initialize them after calling super().

Changelog

3.0.0 (2021-09-07)

• BREAKING CHANGE (TypeScript): registerEvent<(arg: number) => any>() now is registerEvent<[number]>()
• Add unit tests (run npm test)

2.0.0 (2019-08-06)

• Make methods more type safe. This is a breaking change if used in a TypeScript project (rather than plain JavaScript), as this requires TypeScript 3.0+.

1.1.0 (2018-10-01)

• Add support for ES5.

1.0.0 (2016-07-18)

• Initial release.

License

typed-event-emitter is licensed under the MIT License.