ee.ts

class EventEmitter {
  _handlersMap = new Map<string, Function[]>();

  on(event: string, fn: Function) {
    if (this._handlersMap.has(event)) this._handlersMap.set(event, []);
    const funcs = this._handlersMap.get(event);
    funcs.push(fn);
  }

  emit(event: string, ...args: any) {
    const funcs = this._handlersMap.get(event);
    if (funcs && funcs instanceof Array) {
      for (const fn of funcs) {
        fn(...args);
      }
    }
  }

  removeEventListener(event: string, fn: Function) {
    let funcs = this._handlersMap.get(event) || [];
    const n = funcs.indexOf(fn);
    if (n > -1) funcs.splice(n, 1);
    if (funcs.length === 0) this._handlersMap.delete(event);
  }
}