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Can a Chrome Extension Dynamically Add JS Files to Local Extension Directory? User Upload or Saved From the Web?

I'm wondering if it's possible to for certain JS files to be added to the web extension directory later?
Like say I have an app where users can select certain settings from within the app and those files (js and html files, images or blobs) are somehow added into the extension from the web. Like some sort of ondemand updater without using any native apps but it seems that upgrades are done by the appstores automatically.
I'm reading the files using ajax and adding them to indexeddb but because it could be more than one file that's getting messy.
Say a user wants a certain feature on the extension and there's an html page, js files and images then this gets downloaded to a certain folder inside the installed extension.
function download() { //only saves to downloads directory
var imgurl = "https://www.google.com.hk/images/srpr/logo11w.png";
console.log('download');
browser.downloads.download({url:imgurl},function(downloadId){
console.log("download begin, the downId is:" + downloadId);
});
}
I also tried the chrome download function above but that only works for the downloads folder not the extension folder.
Is there any way to make a custom updater?! I know we can't save to disk but any leniency or workarounds for the extension folder?! Even something silly like making a shell call to some dos (and linux/mac) thing that saves the file to the extension folder. I can fetch the files, just not save them.

Ok so I'll put it as an answer. This is the solution I'm leaning on which works for my scenario and I've listed some alternatives below:
Having the other files as separate extensions and giving the user an install link instead where they can install that extension, then those child extensions talk to the mother extension and they know the address to the resources in their child extension folder, so the mother gets the just the file locations from the children to load those assets from that folder. The child extensions are like bundles of those html and js with a background script which sends the addresses of these items to the mother.
https://developer.chrome.com/extensions/messaging#external
The drawback is that I'll have to see how that affects the urls like if I inject the html page from the child extension folder into the main interface using ajax then I can't use relative url's to any images in that 'cos the urls are relative to the mother extension folder.. I'll have to rewrite the child extension urls with the absolute paths into the html page to load images and js from the child extension html code which has relative urls.
Pros:
Cleaner and more persistent than indexeddb.
Files can be loaded normally from disk.
Cons:
User has to install separate extensions.
URL structure might be a bit confusing, need to rewrite urls if loading html from child. However this is only for image src's and where the javascript is loaded from so it's not such a big deal.
Other Possible Solutions:
Indexeddb which I'm already doing seems to be the preferred way of doing this but I really do not want to store every html asset in indexeddb. The upside is that while extensions need to be installed, this method can be done silently fetching and adding files without user interaction and indexeddb seems to be somewhat persistent. Might still end up using this because it is silent but having to load each asset from a database sounds like a nightmare.
The File Handle Api might have worked if I was working on Firefox only https://wiki.mozilla.org/WebAPI/FileHandleAPI
I haven't tried the shell copy, maybe if I fetch with ajax and then save to disk using some dos function and then doing different save functions for different OS systems.
Filesystem Api only saves to downloads and doesn't work for extensions anyways, so that's useless.
UPDATE
In windows there isn't any sudo, but this worked without admin priveleges for a subfolder (not on the C:\ root though). It would work for a linux only app very nicely. If I just wanted to save a file to a windows machine this might work.
Shell copy method would be to grab the contents of file with ajax from the local or remote location, output to DOS as a stream to save to file on windows. And do this for every operating system with a shell exec command or detect the OS and do that command. This way I can even put the files in the exact folder location.
Like say I make this sort of command from the contents:
//To append you can use >> instead of >
//folder seems necessary, can't save to root without admin
echo the content I want to save > C:\folder\textfile.txt
I thought of calling it using shell exec that only works in nodejs, so digging through the other answers on
How to execute shell command in Javascript
//full code to save file using javascript on windows
var shell = WScript.CreateObject("WScript.Shell");
shell.Run("echo content to save > C:\folder\textfile.txt");
The shell command doesn't seem to work. i can't find what this is for. There doesn't seem to be a shell command in regular javascript for windows. It seems to require IE ActiveX. Doesn't work with Firefox or Chrome.

Extensions can't modify their sources because the browser verifies them and resets/disables the extension if they change. Also, in Firefox the extensions aren't even unpacked.
The solution is actually quite trivial: save the code in any storage (localStorage, chrome.storage.local, IndexedDB) as a string and then add it in your extension page as a standard DOM script element. You'll have to relax the standard CSP a bit for that.

Build URL to data file download with link to folder

I have a web application that triggers actions at the server side which result in the generation of data files.
The so generated data files are stored within a folder at drive different from the one where the Web application is.
What I tried so far is to create a shortcut (Windows Server) next to the Index.html, where the shortcut points to the folder at the second drive.
This solution does not appear to work:
If I copy the data file to the same folder where the Index.html file is and enter navigate to the URL httm://127.0.0.1:324324/Data_File.xlsx I get the file downloaded.
If I enter httm://127.0.0.1:324324/MyShortcut/Data_File.xlsx (where MyShortcut points to a folder in drive D) the attempt fails.
How can I achieve this?
The need to access files in the different drive is essential.

You need to configure your server to serve that folder under different location. The only reason you are able to see your app and access that folder is cause server is set up to serve it ATM, not because you are making the right calls from the front or cause the front is asking nicely.
Don't know what Windows server version you are using and IIS version that goes on it, or are you even using IIS (you most probably do) but depending on what you use you need to do something in a lines of this:
IIS7 config
What you probably wanna do is create virtual folder in IIS. Try looking into it, then if you fail ask a question with proper tags according where are you stuck.
I don't see how this is connected to front-end at all so front end tags wont get you far.
EDIT:
Oh, in that case get a second file server running for that folder? This should be the fastest way, use what you can from this list: list

How to access filename from a folder using JavaScript

I am trying to build a simple website with just an index file and a folder full of icons for our internal purpose. I am making this so that anyone in our team can just access the link and download the icons whenever needed without our help. I am trying to read the icons file name from the folder automatically, so every time we update the folder with new ones we don't have to edit the HTML. I know only JavaScript. Please help me.

An alternative could be to produce a filelist of the files via a script or batch file (depending on OS, something like - in psudeo - ls path/to/images > filelist.txt) which redirect the output to a file that ends up in the same root as the index and images.
This file could then be read via fetch() or XMLHttpRequest() and parsed on client side to provide the basis for the links to the updates files.
This would require an extra step in the pipe-line of course, but could easily be automated using a listener for the image directory that triggers the script, part of your project setup and so forth.

This is not possible. In your case Javascript is running in the browser (client-side). It has no access to the servers filesystem. You need a server-side dynamic web-service (php, node.js, ...)

Update only one file via application cache

Here is my manifest.appcache file.
CACHE MANIFEST
app.js
theme.css
logo.png
How can I force browser renew the app.js file only?

Application cache works slightly different to what you may think.
When a new version of the manifest becomes available, the browser goes through all the files and determines which have changed on the server.
The browser does this by sending the "If-Modified-Since" header with the request.
If the file hasn't been modified, the server will return code 304 (not modified) and the browser will skip the download and move to the next file.
Only files that have been modified get refreshed.
It's also a good idea to include a version or hash in the manifest, so a new manifest is always downloaded and checked.
In example, I use a php script to dynamically generate my appcache.manifest.
The script md5's all the included files to produce a hash/version number that's included in the manifest.

I had a same or similar situation to this.
I needed the browser to refresh the cache of file index.html.
And I could only see it refreshed when in incognito mode, which was not helping me much...
except for understanding why I wasn't seeing my file's update...
Anyway, what helped me was like the following:
Make backup of specific file that needs refreshing
Delete file in project
Run web application (without the file)
Return file to project, and then run application
For me, this worked.
I hope it will help others as well.

How to migrate a single (php||javascript||...) file in production without time constraints

I have simple files (php||javascript||...) running in production
(apache+(php||javascript||...)).
I am trying to think to the proper way of migrating a simple file
while not stopping serving web clients.
Possible influences are:
Apache cached files: I do not know how apache deal with files (php, img, ...). Does it cache them, and check for update timestamp to reload, or does it reload on each http request ?
Linux files are changed in an atomic manner: If I cp a file with new content, apache can only see the full content final save results of my command ?
Apache execution process: Can I pause Apache, holding current requests, while copying new file versions.
I imagine the following:
Have files, like php require_once file, named with versions (ex: ABusinessClassD-v1.0.php), support backward compatibility, and simply do a cp of new files one by one, going from bottom up (database, static files (img, ...), php files, javascript files, ...)
Force refresh browser code on demand.
Imagination != as simple as this != Reality.
Please, can somebody summarize globally simple manual steps to update
a simple file in an apache production, without stopping serving web
clients, in a manual intentionally slow process ?

The only sure way to guarantee no issues when moving over a PHP codebase would be to have two servers or two deployments on the same server.
You have Server 1 which contains your old code. Server 2 is set up with the new code. Then, your DNS records or load balancer/proxy settings are changed so your site is instead served from Server 2.
Or with one server, you configure Apache to serve your application from /path/to/old, and then set up your new version in /path/to/new. Then you change your Apache configuration to use /path/to/new for the application and restart the server.
If you ever need to use version numbers in file names (ABusinessClassD-v1.0.php) then you need to learn about version control software like Git or Mercurial.