VUE Web component inside legacy app results in error "_Ctor, object is not extensible" - vue.js

Question

I'm having trouble importing my custom component in my legacy app.
I pre-compiled my SFC as a webcomponent with vue-cli builder, and I import inside my main.js file this way :
import * as HelloWorld from '../dist/hello-world.js'
Vue.component('hello-world',HelloWorld); //if I add my component globally (same _Ctor error)
Then I load my app on a container div :
var app = new Vue({
el:"#container",
data: {
test: 'Vue is init !' //just a test to validate init
},
components:{
HelloWorld //my web component locally (same _Ctor error)
}
});
When my app load, I get this JS error...
I noticed that when the page is loaded without the following component tag :
<hello-world></hello-world>
no error is thrown and if I add the component tag through JS after the page is loaded, component is properly working.
If I add this component outside of my Vue.el (#container) scope, it's working too.
However, I would like to add this component to #container.
I import Vue 2 through CDN.
Seems like a loading or building error but I can't get it.
Thanks for your help.
hello-world.js is a precompiled .VUE file with vue-cli, just a test file catching some events :
<template>
<h1 v-on:click="clickon"
v-on:mouseenter="addone"
>{{msg}}</h1>
</template>
<script>
export default {
name: "HelloWorld",
data() {
return {
msg: 'Hello world!'
}
},
methods : {
clickon: function () {
// `this` inside methods points to the Vue instance
alert('Clicked')
},
addone: function(){
this.msg = 'Mouse entered'
},
}
}
</script>
<style>
h1{
color:red;
}
</style>
Precompiled with :
vue build --target wc HelloWorld.vue

Answer 1

Got it working by building it with --target lib and importing my JS file with:
import '../dist/HelloWorld.umd.js';
Then it can be added to my Vue instance with:
components:{
"hello-world":HelloWorld
}
Seems to be the right way to do it; web components can't be imported this way.