I am using Eclipse Oxygen.
I have web features already installed, I think some packages are missing for javascript files.
When I try to create a new javascript file, I see that there is no javascript file. How to add this feature into eclipse?
screenshot:

You just look in the wrong "folder" ("Web") to create a new JavaScript-file, the proper path is "JavaScript > JavaScript Source File".
You can also take advantage of the search in the Wizards when you type the desired search term at
type filter text.