Implement Event Emitter

Implementing an event emitter in JavaScript involves creating a class or object that can handle events. This typically includes methods for adding event listeners, emitting events, and removing event listeners. Here's a basic example to illustrate how you can implement an event emitter in JavaScript:

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

  // Method to subscribe to an event
  on(event, listener) {
    if (!this.events[event]) {
      this.events[event] = [];
    }
    this.events[event].push(listener);
  }

  // Method to emit an event
  emit(event, ...args) {
    if (this.events[event]) {
      this.events[event].forEach((listener) => {
        listener(...args);
      });
    }
  }

  // Method to remove an event listener
  off(event, listenerToRemove) {
    if (this.events[event]) {
      this.events[event] = this.events[event].filter((listener) => {
        return listener !== listenerToRemove;
      });
    }
  }
}

// Example usage
const emitter = new EventEmitter();

// Listener function
function logData(data) {
  console.log(data);
}

// Subscribe to an event
emitter.on("data", logData);

// Emit the event
emitter.emit("data", "some data"); // Output: 'some data'

// Unsubscribe from the event
emitter.off("data", logData);

// Emitting the event again will have no effect as the listener has been removed
emitter.emit("data", "some data");

In this example, the EventEmitter class has three methods:

• on(event, listener): Registers a listener for a given event.
• emit(event, ...args): Triggers the event, calling all registered listeners with provided arguments.
• off(event, listener): Removes a specific listener from an event.

This is a simplified version of what libraries like Node.js provide, but it demonstrates the core concept of an event emitter in JavaScript.