10.x soon will get a LTS badge [1], so we can expect 10.x (not 11.x) will be added into 19.04 apt repository.

nvm is probably the easiest way to install it, but of course, you can do it manually:

1. mkdir -p ~/apps/

2. Download tar.gz and extract it to ~/apps/

3. Change $PATH variable to include the bin directory

    NODEJS_DIR="node-v8.12.0-linux-x64" # Change version to appropriate 
    export PATH=$PATH:${HOME}/apps/${NODEJS_DIR}/bin

4. Validate "installation" by version check

[1]: https://github.com/nodejs/Release#release-schedule

Edit: There is also a snap package with nodejs - https://nodesource.com/blog/announcing-node-js-snap-linux-us... but there is 12.x (edge channel) not 11.x

    snap info node