Error: unresolved variable $bus and "typeerror: cannot read property '$on' of undefined“

Errors are reported as follows ：

reason

No installation vue-bus plug-in unit

resolvent

$ yarn add vue-bus
$ npm install vue-bus --save

stay main.js In file

import Vue from 'vue';
import VueBus from 'vue-bus';
 
Vue.use(VueBus);