This is a webpack loader. A tiny file with Webpack utilities that are needed to load the other files.
This is where the action happens. This file contains all your code.
It contains all the polyfills you declare in your polyfills.ts file.
It contains the scripts you declare in the scripts section of your angular.json file
"scripts": [ "../node_modules/jquery/dist/jquery.min.js", "../node_modules/bootstrap/js/alert.js", "../Scripts/global-error-handler.js", "../Scripts/responsive-bootstrap-toolkit.js" ],