After the vue export default is exposed, how to call the methods in the methos inside the vue externally?

app.vue

export default {
  data() {
    return {

    }
  },
  methods: {
    Teaching(){
      alert("")
    }
  }
};

a.js

import Vue from "vue"
import App from "./app"
const app = new Vue({
  el: "-sharpapp",
  render: h => h(App)
})

a.html

<!DOCTYPE html>
<html>

<head>
    <title></title>
</head>

<body>
    <div id="app"></div>
</body>

</html>
The

code is the
above. Now I want to write a function in a.html . This function needs to call the Teaching function in methods of vue in app.vue , which looks something like this:

a.html

<!DOCTYPE html>
<html>

<head>
    <title></title>
</head>

<body>
    <div id="app"></div>
    <script>
        function iframe_connect(){
            //Teaching
            app.Teaching()//
        }
    </script>
</body>

</html>

do not know what to do, ask for advice

Feb.28,2021

the rendering function is written like this

h(App, {
    ref: 'app'
})

then call

through app.$refs.app.Teaching ()
MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1bf2a2d-30b5b.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1bf2a2d-30b5b.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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