Uninstall Node.JS using Linux command line?

For Ubuntu 12.04:

sudo apt-get remove nodejs

This will uninstall nodejs as well as npm.

Edit: If you know which package manager was used to install, it is best to uninstall with the same package manager. Examples for apt, make, yum are in other answers.

This is a manual approach:

Running which node will return something like /path/bin/node.

Then run cd /path

This is all that is added by Node.JS.

rm -r bin/node bin/node-waf include/node lib/node lib/pkgconfig/nodejs.pc share/man/man1/node.1

Now the only thing I don't know about is npm and what it has installed. If you install npm again into a custom path that starts off empty, then you can see what it adds and then you will be able to make a list for npm similar to the above list I made for node.