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How to create Event Bus in Vue 3?
In Vue 2, it was:
export const bus = new Vue();
bus.$on(...) bus.$emit(...)
In Vue 3, Vue is not a constructor anymore, and Vue.createApp({}); returns an object that has no $on and $emit methods.
Answer
As suggested in official docs you could use mitt library to dispatch events between components, let suppose that we a sidebar and header which contains a button that close/open the sidebar and we need that button to toggle some property inside the sidebar component :
in main.js import that library and create an instance of that emitter and define as a global property:
Installation :
npm install --save mitt
Usage :
import { createApp } from 'vue'
import App from './App.vue'
import mitt from 'mitt';
const emitter = mitt();
const app = createApp(App);
app.config.globalProperties.emitter = emitter;
app.mount('#app');
in header emit the toggle-sidebar event with some payload :
<template>
<header>
<button @click="toggleSidebar"/>toggle</button>
</header>
</template>
<script >
export default {
data() {
return {
sidebarOpen: true
};
},
methods: {
toggleSidebar() {
this.sidebarOpen = !this.sidebarOpen;
this.emitter.emit("toggle-sidebar", this.sidebarOpen);
}
}
};
</script>
In sidebar receive the event with the payload:
<template>
<aside class="sidebar" :class="{'sidebar--toggled': !isOpen}">
....
</aside>
</template>
<script>
export default {
name: "sidebar",
data() {
return {
isOpen: true
};
},
mounted() {
this.emitter.on("toggle-sidebar", isOpen => {
this.isOpen = isOpen;
});
}
};
</script>
For those using composition api they could use emitter as follows :
Create a file src/composables/useEmitter.js
import { getCurrentInstance } from 'vue'
export default function useEmitter() {
const internalInstance = getCurrentInstance();
const emitter = internalInstance.appContext.config.globalProperties.emitter;
return emitter;
}
And from there on you can use useEmitter just like you would with useRouter:
import useEmitter from '@/composables/useEmitter'
export default {
setup() {
const emitter = useEmitter()
...
}
...
}