We Keep Coding

In JavaScript, what is the main benefit of creating an object in one file, export and use it in other file

I'm learning JavaScript and using AWS SDK from JavaScript.
Reading an IAM example from the documentation, i saw the following pattern:
Create a file name iamClient.js where you instantiate an object and export it.
Create another file where you import the client created above to use it.
What is the main benefit of doing this instead of just create and use the object in the same file ?
I know this is a small example and maybe there is no issue doing everything in the same file, but i'm more curious if this is just for organization/best practice if something bigger is created based on this sample or if there is some sort of technical reason. :)

Well, that's how you'd create a configuration singleton for instance in another language.
Creation of such object might be expensive in time sometimes so you create it once and then just reuse it :)
During testing, if you provide a mock for your iamClient module you're set for all unit-tests (assuming you're using Jest or similar)
It also helps you to not repeat yourself as it's a codesmell

How to include OVRManager in Three.js Scene?

I have created several Three.js/Javascript demo applications that I'm experimenting with in my new Oculus Go. I'm trying to enable the Go Controller to do stuff in my applications, and according to the Oculus Developer Center, the best thing to do is to include OVRManager in my scene so I have access to that API. That sounds good, but for all the documentation (https://developer.oculus.com/documentation/unity/latest/concepts/unity-ovrinput/) I can't see HOW to add OVRManager to my scene! I have not worked with Unity before, but from what I can tell in the documentation there shouldn't be any compatibility issues (should there?)
So what I'd think to do is something like:
<script src="OVRManager.js or something like that"></script>
and then call the functions I need, as I've done with OrbitControls.js and other external dependencies.
But for the life of me, Google searching is just sending me in circles. I see questions posed for C++ and C# but that's of no use to me. How do I get this API working in my Three.js scene? Where do I find it and is there some other way to include it?
Thanks!

Create a unity WebGL build and expose the API you need as public methods in a Unity Script you attach to a GameObject.
Then, you should be able to follow the directions at How to call Unity functions from javascript (copied below) on how to call those methods from your javascript code.
You may be able to use UnityScript, which is vaguely similar to JavaScript, to write the Script if you use an old version of Unity. As of this writing, Oculus recommends version 2017.4.11f1, which I think might still support UnityScript.
One major reason you see so much less UnityScript information is that Unity has been moving away from UnityScript, into only supporting C#.
But regardless of if you code your OVRManager script in C# or UnityScript, Unity will make the methods callable from your JavaScript.
Calling Unity scripts functions from JavaScript
Sometimes you need to send some data or notification to the Unity
script from the browser’s JavaScript. The recommended way of doing it
is to call methods on GameObjects in your content. If you are making
the call from a JavaScript plugin, embedded in your project, you can
use the following code:
SendMessage(objectName, methodName, value);
Where objectName is the name of an object in your scene; methodName is
the name of a method in the script, currently attached to that object;
value can be a string, a number, or can be empty. For example:
SendMessage('MyGameObject', 'MyFunction');
SendMessage('MyGameObject', 'MyFunction', 5);
SendMessage('MyGameObject', 'MyFunction', 'MyString');
If you would like to make a call from the global scope of the
embedding page, see the Code Visibility section below.
Code visibility
Starting from Unity 5.6 all the build code is executed in its own
scope. This approach makes it possible to embed your game on an
arbitrary page without causing conflicts with the embedding page code,
as well as makes it possible to embed more than one build on the same
page.
If you have all your JavaScript code in the form of .jslib plugins
inside your project, then this JavaScript code will run inside the
same scope as the compiled build and your code should work pretty much
the same way as in previous versions of Unity (for example, the
following objects and functions should be directly visible from the
JavaScript plugin code: Module, SendMessage, HEAP8, ccall etc.).
However, if you are planning to call the internal JavaScript functions
from the global scope of the embedding page, you should always assume
that there are multiple builds embedded on the page, so you should
explicitly specify which build you are referencing to. For example, if
your game has been instantiated as:
var gameInstance = UnityLoader.instantiate("gameContainer", "Build/build.json", {onProgress: UnityProgress});
Then you can send a message to the build using
gameInstance.SendMessage(), or access the build Module object using
gameInstance.Module.

Can I invoke any C# method from Universal JS App(.NET)?

I created universal js app in VS2015. I want to know: is it possible to call C# method or create instance of object out Universal js app?
I have been tried to find a solution for 3 hours but I haven't found it yet :(

You can write your C# code in a Windows Runtime Component (WRC) and then consume that WRC from your JavaScript app. The JavaScript app can create objects from the WRC and call the object properties and methods the same way it would call natively JavaScript objects.
See MSDN's Walkthrough: Creating a simple component in C# or Visual Basic and calling it from JavaScript for an example.

Typescript specific methods for saving data online?

I'm thinking about using TypeScript to create an online app, and this will require saving of data online.
What are my options in regards to that?
Is there anything specific to using TypeScript which makes that easier or harder?
Ideally I would use a service like Parse.com to save data, can Typescript be connected to Parse or would I have to rely upon plain JS?

TypeScript runs wherever javascript runs. So
Your options are the same as javascript.
Typescript compiles down to javascript. And it is designed to be a superset of javascript so your javascript will be valid typescript as long as you have variables declared and sometimes types mentioned.
Optional static typing + easier syntax is what makes developing in TypeScript easier.
Static typing makes refactoring and intellisense more reliable. Having an easier syntax for classes / modules means you are more likely to structure your code better.
Yes you can use parse.com with typescript
The recommended way to do that is to create a declaration file describing your javascript code. In the beginning it can be as simple as:
declare var parse:any;
I wrote some guidance on the matter here : http://basarat.github.io/TypeScriptDeepDive/#/declarations
There is a huge resource of declaration files you can find at https://github.com/borisyankov/DefinitelyTyped . In particular check out FireBase : https://www.firebase.com/ and its declaration file : https://github.com/borisyankov/DefinitelyTyped/tree/master/firebase However there isn't one on parse.com yet which is why I mentioned the way to write your own.
Additionally you don't need a declaration file if you do not want any impressive static checking of the typescript code that interacts with the parse.com's api.

C++, win32 api: How to create an html rendering window so that your application would get callbacks from JS calls?

What I need is simple: we have a console app project. We want to have such a function that would open a simple window with nothing but html (default system based) html + js rendering window that would read some default html+js string (form string or const char*). we want to have our own api joined with default js api so that when JS calls some our.function(argument); we would have our C++ application performe some function and for example cout argument. How to create such thing on windows?

CoCreate the MSHTML com object for HTML Documents:
CComPtr spDoc;
HRESULT hr = CoCreateInstance(CLSID_HTMLDocument, NULL, CLSCTX_INPROC_SERVER, IID_IHTMLDocument2, (void**)&spDoc);
Do something like this to read your HTML string and make the document render it.
Depending on what you need in terms of callbacks, you can use the COM DOM Interfaces to traverse the tree, and then sink the appropriate DispInterfaces to get events on the elements you're interested in. I would recommend this.
If what I suggest in #3 isn't good enough for you (and I'd like to hear why) then you can implement your own ActiveX control and have script on your page call methods on it as suggested by raj.

Brushing aside any security / cross browser/platforms concerns you can use implement an ActiveX object in your C++ that you can invoked from javascript.
http://msdn.microsoft.com/en-us/library/7sw4ddf8(v=vs.94).aspx

The host for the WebBrowser control can provide an object that will be accessible to scripts via the external object.
See http://msdn.microsoft.com/en-us/library/aa770041.aspx#GetExternal