Event Emitter

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

  subscribe(event, handler) {
    this.events[event] = this.events[event] || [];
    this.events[event].push(handler);
    return () => this.unSubscribe(event, handler)
  }

  unSubscribe(event, handler) {
    const handlers = this.events[event];
    if (handlers && Array.isArray(handlers)) {
      for (let i = 0; i < handlers.length; i++) {
        if (handlers[i] === handler) {
          handlers.splice(i, 1);
          break;
        }
      }
    }
  }

  emit(event, ...args) {
    (this.events[event] || []).forEach((handler) => {
      handler(...args);
    });
  }
}

// Create a global instance in your app
const globalEvent = new Event()

const handler1 = data => console.log(`handler1(): FOO event emiited with data: ${data}`)
const handler2 = data => console.log(`handler2(): FOO event emiited with data: ${data}`)

// Subscribe to event
globalEvent.subscribe('FOO', handler1)
globalEvent.subscribe('FOO', handler2)

// Emit event when needed
globalEvent.emit('FOO', 'foo') 

// Expected:
// handler1(): FOO event emiited with data: foo
// handler2(): FOO event emiited with data: foo

// Unsubscribe event
globalEvent.unSubscribe('FOO', handler2)

// Then
globalEvent.emit('FOO', 'bar') 

// Expected:
// handler1(): FOO event emiited with data: bar