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How to inject a comment in javascript files using gulp

I try to add a header to every js-file in my project.
The current files are without comments in header.
I want a gulp-task to insert following header to the files:
/*
* New Comment from Gulp-Task
*/
Is there a plugin, already ?
Gulp-Inject is maybe the solution, but I don´t know, how to use it for javascript injection.

This is not a straight answer to your question as it requires some translation to your case, but here is a post on how to update version numbers (in your case, something else) within javascript files.
How to Increment Version Number via Gulp Task?
The second part to this answer is where you'll find your clue.

I found the solution that work for me:
gulp.src(['./**/*.js'])
.pipe(insert.prepend(license))
.pipe(gulp.dest('./'));
It prepend a license head to every .js files in this directory and sub folders.

Revert JavaScript minification using source map

Is it possible to get a proper JavaScript source file if I have the minified file and its corresponding source map?
I know how to prettify JS code (line-breaks and indents), but I would like to get original function / variable names in the file, to be able to better understand the source code.
I would like to get the un-minified JS file to work with, instead of using it to debug in a browser.
PS It is probably somewhere right under my nose, but I didn't manage to find it so far. Sorry if this was already asked!

To work sourcemaps requires both files, minified and original, often original is included in sourcemap file(it has optional sourcesContent for sources that can not be hosted).
Sourcemap is just JSON file, and you can found all needed information inside:
sources - list of source file names,
sourcesContent - optional list
of original sources, if source is not presented it would be null
here.
Utility script, I have written before for this purpose: https://gist.github.com/zxbodya/ca6fb758259f6a077de7

I suggest using the Source Map Visualization tool online to view the original code with both js file and js soucemap file.
https://sokra.github.io/source-map-visualization/

I think you won't be able to completely revert such code to its original state as a lot of information (for example comments or certain variable names) is simply lost in the process. When I understand it correctly for sourcemaps to do this you still need the original file.
If you only aim to prettify the code so its readable again you do not need source maps. Many advanced editors have such functions. For example if you are using Sublime text there is this plugin: https://packagecontrol.io/packages/HTML-CSS-JS%20Prettify which does a great job.
Also see this similar question: How can I debug a minified JS in firebug?

Vim Javascript Autocompletion + Suggestions?

I'm developing on top of OpenLayers.js. My project folder is structured as follows:
project /
|-- OpenLayers.js
|-- map.html
|-- map.js
\-- etc
As you can argue, when I start a new map project, I espect suggestions from Vim on how to complete the code, reading JS classes from all the libraries in the project folder (in this case, just OpenLayers.js).
E.g.:
map = new OpenLayers. --> <C-x><C-o>
map = new OpenLayers.Bounds
.Control
.Map
Selecting one of the suggested classes I should get a kind of autocompletion, like in Aptana. I've installed AutoComplPop and I get a nice automatic menu to select suggestions, but all of them are taken from the current JS file.
Anyway, I've correctly set up Tagbar + node.js + jsctags and I've generated tags file for my project, and added set tags=./tags,./../tags,./*/tags to my .vimrc.
In this case, also, Tagbar maps the current file JS structure but doesn't offer any mapping of the classes coming from other files.
Another probably relevant line in my .vimrc:
autocmd FileType javascript set omnifunc=javascriptcomplete#CompleteJS
I'm struggling to get class and subclass suggestions and now I'm getting a bit confused with all the plugins/piece of software available.
Any hint?
Thank you guys :)

Check out YouCompleteMe and tern_for_vim.
Here's an article about using them together.

Your expectations are a bit too high. Vim is not an IDE like Aptana and the mechanisms used to provide completion are crude.
Did you check that your tags file has OpenLayers.Bounds, OpenLayers.Control or OpenLayer.Map? I can't find OpenLayer.Map and, going through the OpenLayer.debug.js I can't find this function either.
TagBar only works with the current buffer. If you want to show tags for other windows/buffers you'll need another older plugin: TagList.
AutoComplPop doesn't support JS out of the box. How did you set it up? Here is how I did but it still uses <C-x><C-o> while completion from tags is done with <C-x><C-]>.

PyCharm JavaScript References Across .js Files

I'm currently stumped about a problem I'm facing where I can't reference functions and variables from one JavaScript file to the next. I've tried adding all of the JavaScript files as a library in File->Settings->JavaScript->Libraries but with no success - I still get the gray underline for references with, for instance, a hover-over message that reads "Unresolved function or method ".
The strange thing is if I move a copy of the JavaScript files outside of the subversioned project directory and then add that project-external reference to File->Settings->JavaScript->Libraries then the references are found but this solution is not satisfactory because these JavaScript files are updated via subversioning daily (we're in development)
Does anybody have any insight to my problem? If I am not going about this the right way then let me know. What I ultimately want to be able to do is reference variables and functions from specfic JavaScript files across all my JavaScript files so that I can easily follow references (ctrl+leftclick) to insure the parts are fitting together properly.
Thanks!
(P.S. I'm using PyCharm 2.5)

nXhtml (No javascript-mode/eruby-javascript)

I've just installed nXhtml by downloading their zip file, extracting the archive into my home directory and adding (load "/home/spinlock/nxhtml/autostart.el") to my .emacs file. My problem is that when I try to edit a .js.erb file, I'm getting the error:
(No javascript-mode/eruby-javascript)
and I'm not getting the syntax highlighting that I'd expect (for instance, comments are the same color as javascript code). However, when I move the cursor inside a Ruby section of this file, that notice changes to:
(Ruby/eruby-javascript)
which I take as a good sign plus it does look like I've got the proper Ruby syntax highlighting in this part of the buffer (e.g. comments are show in red font).
I assume that I need to add a configuration file that tells emacs how to manage javascript-mode but I have no clue how to do this. Any help would be greatly appreciated.
Thanks!