vue3 响应式的实现过程（Vue3.x使用mitt.js进行组件通信）

npm install --save mitt

import { createApp } from 'vue';
import App from './App.vue';
import mitt from "mitt"

const app = createApp(App)
app.config.globalProperties.$mybus = mitt()

import mitt from 'mitt'
export default mitt()

<template>
  <img alt="Vue logo" src="./assets/logo.png" />
  <HelloWorld msg="Hello Vue 3.0 + Vite" />
</template>

<script>
import mitt from 'mitt'
import HelloWorld from './components/HelloWorld.vue'

export default {
  components: {
    HelloWorld
  },
  setup (props) {
    const formItemMitt = mitt()
    return {
      formItemMitt
    }
  }
}
</script>

import mitt from 'mitt'

const emitter = mitt()

// listen to an event
emitter.on('foo', e => console.log('foo', e) )

// listen to all events
emitter.on('*', (type, e) => console.log(type, e) )

// fire an event
emitter.emit('foo', { a: 'b' })

// clearing all events
emitter.all.clear()

// working with handler references:
function onFoo() {}
emitter.on('foo', onFoo)   // listen
emitter.off('foo', onFoo)  // unlisten

export default function mitt(all) {
 all = all || new Map();

 return {
  all,

  on(type, handler) {
   const handlers = all.get(type);
   const added = handlers && handlers.push(handler);
   if (!added) {
    all.set(type, [handler]);
   }
  },

  off(type, handler) {
   const handlers = all.get(type);
   if (handlers) {
    handlers.splice(handlers.indexOf(handler) >>> 0, 1);
   }
  },

  emit(type, evt) {
   ((all.get(type) || [])).slice().map((handler) => { handler(evt); });
   ((all.get('*') || [])).slice().map((handler) => { handler(type, evt); });
  }
 };
}