In Laravel's framework, it contains quite a lot of PHP functions (php functions), called helpers.
https://laravel.com/docs/5.6/helpers
So how do we customize our own helper in Laravel? It's actually quite simple..
Just add files in autoload in composer.json.

 "autoload": {
        "files": [
            "app/ow_source/_functions.php"
        ],
        "classmap": [
            "database/seeds",
            "database/factories"
        ],
        "psr-4": {
            "App\\": "app/",
            "Ow\\": "app/ow_source/class",
            "Ow\\Model\\": "app/ow_source/model"
        }
    },

In this way, we can call our function anytime and anywhere.