self standing event system

eventSystemMixinStyle.js

    const eventSystem = (obj = {}) => {
        const listeners = new Map;
        function makeHandle(type, func) {
            const eventsys = this;
            return {
                off() {
                    eventsys.off(type, func);
                    return this;
                },
                on() {
                    this.off();
                    eventsys.on(type, func);
                    return this;
                },
                once() {
                    eventsys.once(type, func);
                    return this;
                }
            }
        }
        let esMethods = {
            hasListener(type, func) {
                return listeners.has(type) && listeners.get(type).has(func);
            },
            addListener(type, func) {
                if (!listeners.has(type)) listeners.set(type, new Set);
                listeners.get(type).add(func);
            },
            removeListener(type, func) {
                if (listeners.has(type)) {
                    const typeGroup = listeners.get(type);
                    if (typeGroup.has(func)) typeGroup.delete(func);
                    if (typeGroup.size == 0) listeners.delete(type);
                }
            },
            on(type, func) {
                this.addListener(type, func);
                return makeHandle(type, func);
            },
            once(type, func) {
                if (this.hasListener(type, func)) this.removeListener(type, func);
                const wrap = (...args) => {
                    func.apply(obj,args);
                    this.removeListener(type, wrap);
                }
                this.addListener(type, wrap);
                return makeHandle(type, func);
            },
            off(type, func) {
                this.removeListener(type, func);
                return makeHandle(type, func);
            },
            emit(type) {
                if (listeners.has(type)) {
                    const typeGroup = listeners.get(type);
                    if (typeGroup.size != 0) {
                        const args = Array.prototype.slice.call(arguments, 1);
                        typeGroup.forEach(Listener => {
                            Listener.apply(obj, args);
                        });
                    }
                }
            }
        };

        Object.keys(esMethods).map(method => {
          obj[method] = esMethods[method];
        });
        esMethods = null;
        return obj;
    }