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) {
    let 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
let globalEvent = new Event()
let handler1 = (data) => console.log(`handler1(): FOO event emitted with data: ${data}`)
let handler2 = (data) => console.log(`handler2(): FOO event emitted 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 emitted with data: foo
// handler2(): FOO event emitted with data: foo
// Unsubscribe event
globalEvent.unSubscribe('FOO', handler2)
// Then
globalEvent.emit('FOO', 'bar')
// Expected:
// handler1(): FOO event emitted with data: bar