What @zenofmud said is 100% true however that doesn't mean you cant provide some means of sending a payload to a browser, perform some computation then return the result to node-red.
nodejs and the browser do run in the same runtime but the functionality nodejs provides is NOT available in the browser. Do a search for "run node js in browser"
For example, this solution I provided another user creates a web page where an image is processed client side and passed back to node-red.
The bottom line is, the core of node-red runs in nodejs on top of the v8 engine.
