typescript eventemitter

eventemitter.ts

/**
 * An EventEmitter that implements the NodeJS.EventEmitter interface.
 */
export class EventEmitter implements NodeJS.EventEmitter {

	private _events: { [name: string]: Function[] } = Object.create(null);
	private _maxListeners = 10;

	private _onceListeners: Function[] = [];

	public addListener = this.on;

	private _insertListener(event: string | symbol, listener: Function, prepend: boolean = false): void {
		let eventListeners = this._events[event] = this._events[event] || [];
		if (prepend) {
			eventListeners.unshift(listener);
		} else {
			eventListeners.push(listener);
		}
	}

	public on(event: string | symbol, listener: Function): this {
		this._insertListener(event, listener);
		return this;
	}

	public once(event: string | symbol, listener: Function): this {
		this._onceListeners.push(listener);
		this._insertListener(event, listener);
		return this;
	}

	public removeListener(event: string | symbol, listener: Function): this {
		if (this._events[event] !== undefined) {
			const i = this._events[event].indexOf(listener);
			if (i >= 0) {
				this._events[event].splice(i, 1);
			}
		}
		return this;
	}

	public removeAllListeners(event?: string | symbol): this {
		if (event === undefined) {
			this._events = Object.create(null);
		} else {
			delete this._events[event];
		}
		return this;
	}

	public setMaxListeners(n: number): this {
		this._maxListeners = n;
		return this;
	}

	public getMaxListeners(): number {
		return this._maxListeners;
	}

	public listeners(event: string | symbol): Function[] {
		if (this._events[event] !== undefined) {
			return this._events[event];
		}
		return [];
	}

	public emit(event: string | symbol, ...args: any[]): boolean {
		let hadListeners = false;
		if (this._events[event] !== undefined) {
			for (let i = 0; i < this._events[event].length; i++) {
				const listener = this._events[event][i];

				hadListeners = true;

				const j = this._onceListeners.indexOf(listener);
				if (j >= 0) {
					this._onceListeners.splice(j, 1);
					this._events[event].splice(i, 1);
					i--; // compensate for removal
				}

				listener(...args);
			}
		}
		return hadListeners;
	}


	public listenerCount(event: string | symbol): number {
		if (this._events[event] !== undefined) {
			return this._events[event].length;
		}
		return 0;
	}

	public prependListener(event: string | symbol, listener: Function): this {
		this._insertListener(event, listener, true);
		return this;
	}

	public prependOnceListener(event: string | symbol, listener: Function): this {
		this._onceListeners.push(listener);
		this._insertListener(event, listener, true);
		return this;
	}

	public eventNames(): (string | symbol)[] {
		return Object.keys(this._events);
	}
}