在app下创建辅助目录和文件

    makedir helpers
    touch helpers/function.php

在composer autoload 选项增加file字段

{
  .
  . 
  . 
  "autoload": {
        "psr-4": {
            "App\\": "app/",
            "Database\\Factories\\": "database/factories/",
            "Database\\Seeders\\": "database/seeders/"
        },
        "files": [
            "app/helper/function.php"
        ]
    },
   .
   .
   .
}

重新加载文件

composer dump-autoload