发布者和订阅者完全解耦（通过消息队列进行通信）

适用场景：功能模块间进行通信，如Vue的事件总线。
ES6实现方式：

class eventManager {
    constructor() {
        this.eventList = {};
    }
    on(eventName, callback) {
        if (this.eventList[eventName]) {
            this.eventList[eventName].push(callback);
        } else {
            this.eventList[eventName] = [callback];
        }
    }
    fire(eventName, data) {
        if (
            eventName in this.eventList &&
            Array.isArray(this.eventList[eventName])
        ) {
            this.eventList[eventName].forEach(callback => callback(data));
        } else {
            console.log(`${eventName} is not a resgisted event`);
        }
    }
    off(eventName, callback) {
        if (callback) {
            if (
                eventName in this.eventList &&
                Array.isArray(this.eventList[eventName])
            ) {
                let index = this.eventList[eventName].indexOf(callback);
                index > -1 && this.eventList[eventName].splice(index, 1);
            } else {
                console.log(`${eventName} has not been listen`);
            }
        } else {
            delete this.eventList[eventName]
        }
    }
}
let eventManager1 = new eventManager();
eventManager1.on("event", data => {
    console.log(data);
});
eventManager1.fire("event", "haha");
eventManager1.off("event");