Calling component method in Nuxt from external JS file

Question

I've got an external code that calls on a specific function name someEvent() and I cannot change this file as it belongs externally.

Currently, I have defined the function someEvent() in a separate a.js file in the @/static folder:

function someEvent(e) {
    // I want to call my Nuxt page methods here
}

and included in my head():

export default {
    head() {
         script: [
             { src: 'a.js' }
         ],
    }
}

How do I call my index.vue methods here in this a.js? Or if you have a better method, I welcome any suggestions.