事件总线（发布订阅者模式）

class EventEmitter {
constructor() {
this.cache = {}
}
on(name, fn) {
if (this.cache[name]) {
this.cache[name].push(fn)
} else {
this.cache[name] = [fn]
}
}
off(name, fn) {
let tasks = this.cache[name]
if (tasks) {
const index = tasks.findIndex(f => f === fn || f.callback === fn)
if (index >= 0) {
tasks.splice(index, 1)
}
}
}
emit(name, once = false, ...args) {
if (this.cache[name]) {
// 创建副本，如果回调函数内继续注册相同事件，会造成死循环
let tasks = this.cache[name].slice()
for (let fn of tasks) {
fn(...args)
}
if (once) {
delete this.cache[name]
}
}
}
}

let eventBus = new EventEmitter()
let fn1 = function(name, age) {
console.log(`${name} ${age}`)
}
let fn2 = function(name, age) {
console.log(`hello, ${name} ${age}`)
}
eventBus.on('aaa', fn1)
eventBus.on('aaa', fn2)
eventBus.emit('aaa', false, '布兰', 12)