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class EventEmitter {
  constructor() {
    this._events = this._events || new Map();
  }
}

EventEmitter.prototype.emit = function(type, ...args) {
  const handler = this._events.get(type);
  if (Array.isArray(handler)) {
    handler.forEach(h => {
      if (args.length > 0) {
        h.apply(this, args)
      } else {
        h.call(this)
      }
    })
  } else {
    if (args.length > 0) {
      handler.apply(this, args)
    } else {
      handler.call(this)
    }
  }
}

EventEmitter.prototype.addListener = function(type, fn) {
  const handler = this._events.get(type)
  if (!handler) {
    this._events.set(type, fn);
  } else if (handler && typeof handler === 'function') {
    this._events.set(type, [handler, fn])
  } else {
    handler.push(fn)
  }
}

EventEmitter.prototype.removeListener = function(type, fn) {
  const handler = this._events.get(type)
  if (handler && typeof handler === 'function') {
    this._events.delete(type)
  } else {
    let position
    handler.forEach((h, i) => {
      if (h === fn) {
        position = i
      } else {
        position = -1
      }
    })

    if (position !== -1) {
      handler.splice(position, 1)
      if (handler.length === 1) {
        this._events.set(type, handler[0])
      }
    } else {
      return this;
    }
  }
}