Notepad++ and other similar frugal text editors are more geared towards small projects like Processing sketches and quick file edits.
IDEs like Sublime, Atom, Brackets, Eclipse, etc., are more appropriate for bigger projects.
Firefox and its derivatives browsers can run “.js” code directly under the file:// scheme.
Chromium-based browsers can do it too, though w/ some limitations, if we run it w/ a modified shortcut w/ an “–allow-file-access-from-files” argument: Chrome-allow-file-access-from-file.com/