b-class.js

'use strict';

class EventEmitter {
  constructor() {
    this.events = new Map();
    this.wrappers = new Map();
  }

  on(name, fn) {
    const event = this.events.get(name);
    if (event) event.add(fn);
    else this.events.set(name, new Set([fn]));
  }

  once(name, fn) {
    const wrapper = (...args) => {
      this.remove(name, wrapper);
      fn(...args);
    };
    this.wrappers.set(fn, wrapper);
    this.on(name, wrapper);
  }

  emit(name, ...args) {
    const event = this.events.get(name);
    if (!event) return;
    for (const fn of event.values()) {
      fn(...args);
    }
  }

  remove(name, fn) {
    const event = this.events.get(name);
    if (!event) return;
    if (event.has(fn)) {
      event.delete(fn);
      return;
    }
    const wrapper = this.wrappers.get(fn);
    if (wrapper) {
      event.delete(wrapper);
      if (event.size === 0) this.events.delete(name);
    }
  }

  clear(name) {
    if (name) this.events.delete(name);
    else this.events.clear();
  }

  count(name) {
    const event = this.events.get(name);
    return event ? event.size : 0;
  }

  listeners(name) {
    const event = this.events.get(name);
    return new Set(event);
  }

  names() {
    return [...this.events.keys()];
  }
}

// Usage

const ee = new EventEmitter();

// on and emit

ee.on('e1', (data) => {
  console.dir(data);
});

ee.emit('e1', { msg: 'e1 ok' });

// once

ee.once('e2', (data) => {
  console.dir(data);
});

ee.emit('e2', { msg: 'e2 ok' });
ee.emit('e2', { msg: 'e2 not ok' });

// remove

const f3 = (data) => {
  console.dir(data);
};

ee.on('e3', f3);
ee.remove('e3', f3);
ee.emit('e3', { msg: 'e3 not ok' });

// count

ee.on('e4', () => {});
ee.on('e4', () => {});
console.log('e4 count', ee.count('e4'));

// clear

ee.clear('e4');
ee.emit('e4', { msg: 'e4 not ok' });
ee.emit('e1', { msg: 'e1 ok' });

ee.clear();
ee.emit('e1', { msg: 'e1 not ok' });

// listeners and names

ee.on('e5', () => {});
ee.on('e5', () => {});
ee.on('e6', () => {});
ee.on('e7', () => {});

console.log('listeners', ee.listeners('e5'));
console.log('names', ee.names());