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How to automatically make array of all files in website folder?

Let's say I have a folder of about 100 images on my website called "IMG"
Now let's say I have a div element: <div id="templateDiv"></div>
Using javascript, how would I add all images from "IMG/" into that div without adding <img src="IMG/IMGNAME.jpg"> for every image?
Sorry, I'm not very good at explaining.
Just ignore the fact that would take ages to load.
EDIT
Ok my bad explanation skills have made me change my question.
How do I automatically make array of all files in website directory?

Okay, your question is incredibly unclear, but from reading all your other comments and things, it seems you simply want to get an array that contains the filename of every file in a directory? If that's what you want, then it won't be possible (I don't believe) since only the server knows which files are where, and you can't request the contents of a directory from a server using JavaScript.
However if you were using Node.js on a local directory, then it could be done. But I don't believe that's your case.
That being said, you have three alternative options:
Name every image file 1.png, 2.png, 3.png, etc. Then use a for loop and get each one using (i + 1) + ".png"
If you can't rename the files, but the files are named via user input, you could collect the user's input at the time of file creation and add the name of the newly created file into another file/an array/localStorage so that it could be retrieved later.
If you can't rename the files, but the filenames are also never known to the program that needs them, then you could create an array of all the filenames (manually) and iterate over that to find all the files that you want.
Please, somebody let me know if I'm wrong and if there actually is a way to make a request to a server that tells the client all the files in a directory. That seems incredibly unlikely though.
Another potential solution just came to mind. You could write a PHP script (or Node.js or any server-side language, really) that scans a directory, creates a list of all the filenames there, and then sends that back over HTTP. Then you could simply make an XMLHttpRequest to that PHP file and have it do the work. How does that sound?

What is ctag in javascript loaded files in a webpage?

When I inspect a webpage I can see javascript files with name and a query string attached to their name. Like: jquery-1.9.1.min.js?ctag=0$$16.0.4230.1217.
I googles ctag but didn't find anything useful which I can understand.
I want to know what is the difference between files with ctag and without it?
(jquery-1.9.1.min.js vs. jquery-1.9.1.min.js?ctag=0$$16.0.4230.1217)

When you see http parameters added to the end of a script url it's usually for one of two reasons.
To cache the script in the browser.
Usually a version number is added, the cache can then be forced to update by changing the version. i.e.
http://example.com/js/myscrpt.js?ver=0.4
To send data to the server.
It might be that the script being returned is actually generated server side and the parameter is sending a value that is used in the generation of that script. i.e.
http://example.com/js/myscript.js?userid=935284025805
UPDATE: searching the web, it seems that links deployed on Sharepoint using JSLINK adds a ctag parameter to the urls of javascript files. It's possible the link is from a Sharepoint site, see here and here for Sharepoint questions about the added ctag

Getting the file extension without knowing it's name

I need to know if there is a way to retrieve the real file extension without parse the filename.
In my code I split the file using the function split(filename, ".") then i get the last element of the array that the function returns.
Now, if I create a .pdf file called, for example test_file.pdf, the previous method works perfectly, but if i rename my file to test_file(without extension) I cannot retrieve the extension even if I know that the file is a PDF.
For example, if i rename test_file.pdf to text_file.jpg how can I recognize that the file is still a pdf and not an image file with .jpg extension?
I would like to know if there is a way to obtain this information, maybe using file metadata or other information related to the file.
I'm looking for a Javascript solution because I have to check the extension when I upload the file using a form (client side) but even a Java solution could be fine, can you help me?
Thank you in advance!

Look at this post and the marked answer: Get real file extension -Java code
I guess it's just what you need.

What does the "?" sign mean in a request for a static JS file?

I've seen that a lot and I just don't know what it means. This, for example:
<script src="http://server.com/file.js?y=2345678" type="text/javascript"></script>
If it is in deed possible to 'catch' the value of 'y' in the javascript file, how would that be?
Thank you.
PS. I know what mod_rewrite is and that is not the answer, just in case :)

This is to force the browser not to cache the file, by making it believe that it is a dynamic file with get parameter rather than a static one.

This is often used to facilitate caching of the JS file. You set a far-future Expires header which means the browser may cache it for a very long time. If you change something in the file you also update the number in the querystring, which will make the browser refetch the file. This works because caching is for unique filenames and the querystring is part of the filename (as far as the browser is concerned).
A similar approach to this is to use rewrite rules in the web server to have some part of the file name which it doesnät care about. Here's a Nginx rule to show what I mean:
rewrite ^/style\..*\.css$ /style.css;
I use this rule to have filenames like style.42750cad6.css, which always points to the file style.css. The text in the middle is changed whenever I change style.css. The difference between the first approach is that this does not use the querystring so the caching will work in more browsers.

ok the way i see it in two ways.
it can be used to load js without caching
for every request to the server, the server might log information(if logging is enabled), if i am using it for analytics i can therefore use a different parameter for locations and from the log i can analyse and get required details.

Javascript redirect to dynamically created HTML

I have a javascript routine that dynamically creates an HTML page, complete with it's own head and script tags.
If I take the contents of the string and save it to a file, and view the file in a browser, all is well, but if I try document.write(newHTML), it doesn't behave the same. The javascript in the header of the dynamic newHTML is quite complicated, and I cannot include it here... But please believe me that it works great if I save it to a file, but not if I try to replace the current page with it using document.write. What possible pitfalls could be contributing to this that I'm not considering? Do I possibly need to delete the existing script tags in the existing header first? Do I need to manually re-call onLoad??
Again, it works great when the string is saved to, for example, 'sample.html' and browsed to, but if I set var Samp="[REAL HTML HERE]"; and then say document.write(Samp); document.close(); the javascript routines are not executing correctly.
Any hints as to what I could be missing?
Is there another/better way to dynamically replace the content of the page, other than document.write?
Could I somehow redirect to the new page despite the fact that doesn't exist on disk or on a server, but is only in a string in memory? I would hate to have to upload the entire file to my server simply to re-download again it to view it.
How can I, using javascript, replace the current content of the current page with entirely new content including complex client-side javascripting, dynamically, and always get exactly the same result as if I saved the string to the server as an html file and redirected to it?
How can I 'redirect' to an HTML file that only exists as a client-side string?

You can do this:
var win=window.open("") //open new window and write to it
var html = generate_html();
win.document.write(html)
win.document.close();

Maybe eval() function would help here? It's hard to give ansver without seeing the code.

Never tried this, but i think it should be possible. Some thoughts on what might make it work:
Make sure the document containing your js is sent with the correct headers / mimetype / doctype
Serve the javascript in a valid way, for example by sending a w3c valid page containing the script tag.
Maybe then it works. If not, try to erase the current html before writing the new one.
Also, it might be helpful to look how others managed to accomplish this task. If i remind it correctly, the google page is also essentially a short html page with a bunch of js.