### 发布／订阅模式
[微信小程序跨页面通信解决思路](https://aotu.io/notes/2017/01/19/wxapp-event/)
~~~
//event.js
class Event {
on (event, fn, ctx) {
if (typeof fn != "function") {
console.error('fn must be a function')
return
}
this._stores = this._stores || {}
;(this._stores[event] = this._stores[event] || []).push({cb: fn, ctx: ctx})
}
emit (event) {
this._stores = this._stores || {}
var store = this._stores[event], args
if (store) {
store = store.slice(0)
args = [].slice.call(arguments, 1)
for (var i = 0, len = store.length; i < len; i++) {
store[i].cb.apply(store[i].ctx, args)
}
}
}
off (event, fn) {
this._stores = this._stores || {}
// all
if (!arguments.length) {
this._stores = {}
return
}
// specific event
var store = this._stores[event]
if (!store) return
// remove all handlers
if (arguments.length === 1) {
delete this._stores[event]
return
}
// remove specific handler
var cb
for (var i = 0, len = store.length; i < len; i++) {
cb = store[i].cb
if (cb === fn) {
store.splice(i, 1)
break
}
}
return
}
}
~~~
