promisify-node | Wrap Node-callback functions to return Promises | Reactive Programming library

Node.js doesn't get bundled with the source code of apps. The package.json might have a section called "engines" in which it will state what version you should be using.

If the root package.json doesn't have the "engines" section, then it may be posable that the some of the dependencies do say which version they require to be used. It would be kind of annoying going through each one to check, so a good way would be just to download a version of Node and run npm install. If everything works, then you know that the Node version the app was created in is most likely older (its a bit tedious, I know).

Another thing you could look for (but might not be to helpful) would be to check when the files of the source code were created (especially the package.json file), and find the Node version that was released around that time. This wont be as accurate as the first method but it will give you a working version of Node.

When it comes down to it though, its probably always best to use the most up to date version (or the most recent LTS version) as they come with all the latest security patches and improvements.