observerDecorator

let observerDecorator = (function () {
    let eventList = {}

    return function (obj) {
        obj.addEvent = (event, fn) => {
            if(!eventList[event]) {
                eventList[event] = []
            }

            if(eventList[event].indexOf(fn) === -1) {
                eventList[event].push(fn)
            }
        }

        obj.dispatchEvent = (event) => {
            if(!eventList[event]) {
                return
            }

            for(let fn of eventList[event]) {
                fn()
            }
        }
    }
})()

class Worker {}
class Boss {}
//

let worker = new Worker()
let boss = new Boss()

observerDecorator(worker)
observerDecorator(boss)

let salary = () => {
    console.log('thank you boss!')
}
worker.addEvent('salary', salary)
worker.addEvent('salary', salary)
boss.dispatchEvent('salary')