systemjs VS RequireJS

I would like to upgrade my existing Rails and Angular 1.x application. I'm following the ng-upgrade documentation and seeing that there are many dependencies including systemjs, typescript, tsd and a few other javascript libraries. Ideally there would be a angular-2 gem that would have all the dependencies but I'm not able to find that. Next I looked for gem's for each dependency but there isn't one for tsd.

There's also https://github.com/systemjs/systemjs if you want more of a ponyfill approach. FWIW bundlers also don't use the browser's functionality to load modules...

A module loader interprets and loads a module written in a certain module format at runtime. Popular examples are RequireJS and SystemJS.

There is a library called requirejs (https://requirejs.org/) that accomplishes what I am referring to. However, this is essentially similar to the situation in PHP prior to version 5.3 - a solution implemented at the level of a separate library rather than at the language level.

Webpack is the most popular bundler and it followed on the heels of Require.js, Rollup, and similar solutions. But the learning curve for a tool like webpack is steep. Getting started with webpack isn’t easy due to its complex configurations. As a result, in recent years another solution has emerged. This tool is not necessarily a front-runner, but an easier-to-digest alternative on the front-end module bundler landscape. Introducing Parcel.js.

I have a number of JavaScript "classes" each implemented in its own JavaScript file. For development those files are loaded individually, and for production they are concatenated, but in both cases I have to manually define a loading order, making sure that B comes after A if B uses A. I am planning to use RequireJS as an implementation of CommonJS Modules/AsynchronousDefinition to solve this problem for me automatically.

This may be a dumb question for web guys. But I am a little confused over this. Now, I have an application where I am using a couple of Javascript files to perform different tasks. Now, I am using Javascript bundler to combine and minify all the files. So, at runtime there will be only one app.min.js file. Now, Requirejs is used to load modules or files at runtime. So, the question is if I already have all things in one file, then do I need requirejs? Or what is a use case scenario where I can use requirejs and/or bundler?

AMD (Asynchronous Module Definition), is a pattern to define and consume module. It is implemented by RequireJS library. AMD provides a define function to define module, which accepts the module name, dependent modules’ names, and a factory function:

While reading RequireJS' source code, I stumbled upon this function:

A lot of SPA frameworks and libraries also were developed. We can find out some of its on the internet. They are AngularJs, Reactjs, BackboneJs, DurandalJs,.. and a lot of third party components to make the Javascript coding more easy like RequireJs, Amplifyjs, BreezeJs...