Bdtyktl

Normal installation would be sudo apt install nodejs to install Node.js and then sudo apt install npm to install Node Package Manager. However, upon doing so, npm -v says 3.5.2. To upgrade normally, I would do sudo npm install -g npm, which updates to the latest version (which, at the time of writing this article, is 6.0.1).

When I do a which npm, I get /usr/local/bin/npm, however apt installs a symlink at /usr/bin/npm. If I sudo apt purge npm to remove npm, it still leaves the npm version of npm at /usr/local/bin/npm, however npm -v says -bash: /usr/bin/npm: No such file or directory.

Many articles say to use a PPA to install nodejs, but I think there should be a native way to do this through apt.

DigitalOcean instructions on installation normally and through PPA: https://www.digitalocean.com/community/tutorials/how-to-install-node-js-on-ubuntu-18-04

TecAdmin instructions on installation through PPA: https://tecadmin.net/install-latest-nodejs-npm-on-ubuntu/

The way I found is to purge npm through sudo apt purge npm, then simply recreate a symlink to the global installation via ln -s /usr/local/bin/npm /usr/bin/npm. After that fix, npm -v returns 6.0.1 as expected.

To have control on installed npm version, I always use nvm (node version control). You can install it through the instructions here: https://github.com/creationix/nvm
Then by following command install the latest npm on your computer:

nvm install node

TLDR: This problem is caused by Bash caching the path of the npm command, and can be solved by hash -d npm. You don't even need to deal with apt purge unless you want to.

Explanation

Here were my steps for getting a new npm version on Ubuntu. First, do the installation as OP describes:

$ sudo apt-get install npm

(...apt installation of npm was successful...)

$ npm -v

3.5.2

$ command -v npm

/usr/bin/npm

$ sudo npm install -g npm

(...npm installation of npm was successful...so far, so good)

You can see that the new version is already working fine in /usr/local/bin/npm, but unfortunately the Bash cache still has /usr/bin/npm:

$ /usr/local/bin/npm -v

6.4.1

$ npm -v

3.5.2

$ command -v npm

/usr/bin/npm

$ type npm

npm is hashed (/usr/bin/npm)

To fix the problem, clear it from the Bash cache (do this in all open shells):

$ hash -d npm

Now the new version works as desired:

$ npm -v

6.4.1

$ command -v npm

/usr/local/bin/npm