无法使用旧的JS函数与Laravel 5.7刀片模板中的一些jQuery与webpack - 找不到方法

I'm using Laravel 5 Boilerplate that comes with some structure already done.

I want to call a simple JavaScript method from the blade. Here's what I did:

1) Created file called test123.js

content of test123.js:

function test123() {
    $(document).ready(function () {
        console.log('hello from test123');
    });
}

2) I opened the existing app.js and added:

import './test123';

3) I called npm dev run - all green, all OK.

4) In blade index.blade.php I typed:

@push('after-scripts')
    <script>
        test123();
    </script>
@endpush

I went to compiled file:

<script src="http://foo.local/js/backend.js?id=8dbe74e012c3122422da"></script>

My method is there:

however it's not visible.

I guess it's about scopes? I don't want to make it window.test123. Should I? I just want define good old JS / jQuery method and invoke it only when needed in specific templates.

"Modern" JS is not my strong point as I find it very convoluted. I haven't touched default webpack.mix.js.

mix.setPublicPath('public');

mix.sass('resources/sass/frontend/app.scss', 'css/frontend.css')
    .sass('resources/sass/backend/app.scss', 'css/backend.css')
    .js('resources/js/frontend/app.js', 'js/frontend.js')
    .js([
        'resources/js/backend/before.js',
        'resources/js/backend/app.js',
        'resources/js/backend/after.js'
    ], 'js/backend.js')
    .extract([
        'jquery',
        'bootstrap',
        'popper.js/dist/umd/popper',
        'axios',
        'sweetalert2',
        'lodash',
        '@fortawesome/fontawesome-svg-core',
        '@fortawesome/free-brands-svg-icons',
        '@fortawesome/free-regular-svg-icons',
        '@fortawesome/free-solid-svg-icons'
    ]);

Please help me to achieve this simple thing. I know the solution probably is not difficult but I don't know what to do…

Thank you.

Edit 1: I almost forgot. Here's the Boilerplate structure:

Edit 2: User brk requested some more screenshots:

Try exporting the function explicitly:

export function test123() {...}

and later import it:

import 'test123' from './test123';

You can try do this with require.js

 //declare fn test123
 test123(){ ...do something}
 module.exports.test123 = test123;

and then

 let test123 = require('./test123');

Here you can find more information about using require.js in browser with jquery https://requirejs.org/docs/jquery.html