Ctrl+/ on Windows makes whatever you have selected a comment, e.g.:
test
turns into
// test
I’d like to have
test
turn into
//test
without the space between the comment and the thing being commented out. Is this possible to configure?
Ctrl+/ on Windows makes whatever you have selected a comment, e.g.:
test
turns into
// test
I’d like to have
test
turn into
//test
without the space between the comment and the thing being commented out. Is this possible to configure?
Yes.
Edit Comments.tmPreferencesfile of the language you want tweaked (e.g. Comments (C++).tmPreferences) and go crazy 
Awesome! I’m super new, can you tell me how to track down the Comments.tmPreferences files on my computer to edit?
Edit: * I am using Sublime Text 3
OK so I am getting closer, I opened Comments.tmPreferences for JavaScript and changed the TM_COMMENT_START to be:
<dict>
<key>name</key>
<string>TM_COMMENT_START</string>
<key>value</key>
<string>//</string>
</dict>
I saved my changes and then closed Subkime Text and reopened it. My commenting shortcut (Ctrl+/) still adds the extra space! I confirmed that the document type is JavaScript in the bottom right corner.
Am I missing something?
Works for me. (see my Edit at the end)
Do you have modified the right one?
…\SublimeText\Packages\JavaScript.sublime-package
Or better, a copy of them, copied before to User folder:
…\SublimeText\Data\Packages\User\JavaScript.sublime-package
The manual way:
Copy “JavaScript.sublime-package”
from “…\SublimeText\Packages”
to “…\SublimeText\Data\Packages\User”
Add an zip extension. ( “.\SublimeText\Data\Packages\User\JavaScript.sublime-package.zip”)
Unzip.
Rename the new folder to “JavaScript.sublime-package-unpackt”
Go inside of “.\SublimeText\Data\Packages\User\JavaScript.sublime-package-unpackt”
Open “Comments.tmPreferences”, modify and save.
Zip all content inside of the folder “JavaScript.sublime-package-unpackt”
“.\SublimeText\Data\Packages\User\JavaScript.sublime-package-unpackt\JavaScript.sublime-package.zip”
Remove the zip extension.
“.\SublimeText\Data\Packages\User\JavaScript.sublime-package-unpackt\JavaScript.sublime-package”
Move the file “JavaScript.sublime-package” up to “…\SublimeText\Data\Packages\User”
You can delete the folder “\User\JavaScript.sublime-package-unpackt” and the older “\User\JavaScript.sublime-package.zip”
Edit:
now I also could not go back to "// ", even I removed all of my modifications. 
Solution: Delete the Cache folder “…\SublimeText\Data\Cache\JavaScript” (since I don’t know if that folder would have something useful in it, just move them only instead of actual deleting)