Event Emitter Pattern

Lightweight event system for decoupled communication between components. Useful for custom events and pub-sub patterns.

JavaScript7/16/2025

#patterns#events#pub-sub

JavaScript

class EventEmitter {
  constructor() {
    this.events = {};
  }
  
  on(event, callback) {
    if (!this.events[event]) {
      this.events[event] = [];
    }
    this.events[event].push(callback);
  }
  
  off(event, callback) {
    if (!this.events[event]) return;
    this.events[event] = this.events[event].filter(cb => cb !== callback);
  }
  
  emit(event, ...args) {
    if (!this.events[event]) return;
    this.events[event].forEach(callback => callback(...args));
  }
  
  once(event, callback) {
    const wrapper = (...args) => {
      callback(...args);
      this.off(event, wrapper);
    };
    this.on(event, wrapper);
  }
}

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