A simple custom event hub for simple DOM apps

CustomEventHub.js

let CustomEvent = window.CustomEvent;

if (typeof CustomEvent !== "function") {
    // Internet Explorer
    CustomEvent = function(name, options = {}) {
        let {
            bubbles = false,
            cancelable = false,
            detail
        } = options;
        
        let evt = document.createEvent("CustomEvent");
        evt.initCustomEvent(name, bubbles, cancelable, detail);
        return evt;
    };
}

class CustomEventHub {
    
    constructor(target) {
        if (typeof target === "string") {
            let selector = target;
            target = window.document.querySelector(selector);
            if (!target)
                throw new Error(`No element matching selector "${ selector }" found`);
        } else if (!target) {
            target = window.document.createElement("div");
        } else {
            target = Object(target);
        }
        
        this._target = target;
    }

    get target() { return this._target; }

    listen(event, fn) {
        if (typeof fn !== "function")
            throw new TypeError(fn + " is not a function");
            
        this._target.addEventListener(event, fn, false);
        return _=> { this._target.removeEventListener(event, fn, false) };
    }

    dispatch(event, options = {}) {
        return Promise.resolve().then(_=> {
            if (typeof event === "string")
                event = new CustomEvent(event, options);
            
            this._target.dispatchEvent(event);
            return event;
        });
    }

    static get CustomEvent() { return CustomEvent }
    
}