How can I make my Helper Class globally accessible in VueJS?

Hi as Andrew v said you can directly use the prototype key and add it to your Vue app for Vue2:

import Vue from 'vue'

import { HelperClass } from '@/assets/js/myFunc.js';

Vue.prototype.$HelperClass = HelperClass

And then

this.$HelperClass.myFunc()

How to import my own class or method globally in Vue?

Otherwise for vue 3:

export default class {
    myFunc() {
        alert("Exported Class")
    }
}

You can provide it for all your app using provide/inject:

import { createApp } from 'vue'
import App from './App.vue'
import HelperClass from './class'

const helperClass = new HelperClass();

createApp(App)
    .provide('helperClass', helperClass)
    .mount('#app')

import { inject } from 'vue'

export default {
  setup() {
    const message = inject('helperClass')
    console.log(message.myFunc())
    return { message }
  }
}

Or in each .vue file needed with Composition Api:

import { ref } from 'vue'
import HelperClass from './whateveryourpathis'
export default {
  setup() {
    const helperClass = ref(new HelperClass())
    console.log(helperClass.value.myFunc())
  }
}

Or if you use the setup tag on the script

<script setup>
  import { ref } from 'vue'
  import HelperClass from './whateveryourpathis'
  const helperClass = ref(new HelperClass())
  console.log(helperClass.value.myFunc())
</script>