So I see three possible reasons for the problem:
The file was marked as 'Plain text'
There is a pattern for 'Text files' file type that matches this file (or back: file type 'JavaScript' exclude this file name). See image below
- There is a custom plugin that overrides default behavior for files with this name (unlikely)
Updated: after several years I've found one more reason for the behavior and most likely it the main source of the issues. When you create a file without any extensions the "Register New File Type Association" is appeared. And you can accidentally specify a new file type, for some file name. It is can be fixed with (2) but it is the reason why the pattern was added there.
Note: the solution works for all IDEA-based IDEs: IntelliJ IDEA, WebStorm, RubyMine, PyCharm, PhpStorm.
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