I started a new project and wanted to use node/npm inside of WSL2. However, when I tried to run npm inside of either Ubuntu 18 or 20, I got this error message:

mark@LAPTOP:~$ npm
-bash: /mnt/c/Program Files/nodejs/npm: /bin/sh^M: bad interpreter: No such file or directory

After a whole lot of searching, I came across this web page, https://stackoverflow.com/questions/63716587/in-wsl2-ubuntu-20-04-for-windows-10-nodejs-is-installed-but-npm-is-not-working which suggested updating the ~/.bashrc file to look like:

# strip out problematic Windows %PATH%
PATH=$(echo "$PATH" | sed -e 's/:\/mnt.*//g')

I added that to the VERY end of the file, and rebooted.

The next time I tried to run npm, I got this successful message instead:

mark@LAPTOP:~$ npm

Usage: npm <command>

where <command> is one of:
    access, adduser, audit, bin, bugs, c, cache, ci, cit,
    clean-install, clean-install-test, completion, config,
    create, ddp, dedupe, deprecate, dist-tag, docs, doctor,
    edit, explore, fund, get, help, help-search, hook, i, init,
    install, install-ci-test, install-test, it, link, list, ln,
    login, logout, ls, org, outdated, owner, pack, ping, prefix,
    profile, prune, publish, rb, rebuild, repo, restart, root,
    run, run-script, s, se, search, set, shrinkwrap, star,
    stars, start, stop, t, team, test, token, tst, un,
    uninstall, unpublish, unstar, up, update, v, version, view,
    whoami

npm <command> -h  quick help on <command>
npm -l            display full usage info
npm help <term>   search for help on <term>
npm help npm      involved overview

Specify configs in the ini-formatted file:
    /home/mark/.npmrc
or on the command line via: npm <command> --key value
Config info can be viewed via: npm help config

npm@6.14.4 /usr/share/npm