Yeah, but node.js is a framework, not pure js, and I suspect it doesn't do DOM-related stuff. jQuery is probably better suited for general in-browser javascript.
This reasoning seems fundamentally confused, so I feel like clarifying some concepts:
On Runnable you can create basic client-side JavaScript files to be run in the browser (without jQuery) and do window and DOM manipulations.
Node.js isn't a framework for the browser (like jQuery), but a server application platform (with a bunch of objects and functions).
"Pure js" doesn't exist as an environment. It runs within a parent environment (e.g. a browser or a server) and manipulates the global objects in that environment.
JavaScript is just a language specification, and can be implemented in any environment. (For instance, it's implemented in Adobe Illustrator.)
Ok, got you. If you use the "Create New" button in the top right corner, you get the option to create a "JS" project.
The project template comes with jQuery pre-installed. However, it can easily be removed.
I guess the people behind Runnable assumes that it's more convenient to have to remove jQuery than having to add it for each new JS project, and personally I agree with that assumption.