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class EventEmitter {  constructor() {    this.observers = {};  }
  on(events, listener) {    events.split(' ').forEach((event) => {      this.observers[event] = this.observers[event] || [];      this.observers[event].push(listener);    });    return this;  }
  off(event, listener) {    if (!this.observers[event]) {      return;    }
    this.observers[event].forEach(() => {      if (!listener) {        delete this.observers[event];      } else {        const index = this.observers[event].indexOf(listener);        if (index > -1) {          this.observers[event].splice(index, 1);        }      }    });  }
  emit(event, ...args) {    if (this.observers[event]) {      const cloned = [].concat(this.observers[event]);      cloned.forEach((observer) => {        observer(...args);      });    }
    if (this.observers['*']) {      const cloned = [].concat(this.observers['*']);      cloned.forEach((observer) => {        observer.apply(observer, [event, ...args]);      });    }  }}
export default EventEmitter;