Oficial npm.fish

This is deprecated.

fish-npm-scripts-completion

npm + TAB => list of commands available for npm
npm run + TAB => list of scripts from package.json

Installation

Be sure to have ~/.config/fish/completions folder and then run: test -f ~/.config/fish/completions/npm.fish;or curl https://raw.githubusercontent.com/sudodoki/fish-npm-scripts-completion/master/npm.fish ~/.config/fish/completions/npm.fish

or just download npm.fish and put it into ~/.config/fish/completions or any other folder in $fish_complete_path variable

Restart your fish and it should run.

Fish versions supported

Confirmed this is working with fish v2.2.0 (you can get version of fish by running fish -v). Had issues with prior version and complete -e of arguments (if you want to make it work with fish < 2.2.0 I assume you will need to modify fish_complete and complete -e each word in string)