node.js - Is it possible to install npm package only if it has not been already installed?

Question

Is it possible to install npm package only if it has not been already installed?

I need this to speed up test on CircleCI, but when I run npm install [email protected] etc. it always downloads things and installs them from scracth, however, node_modules folder with all modules is already present at the moment of running commands (cached from previous build) and protractor --version etc. shows the needed version of the package.

Its perfect to have some one-line command like this:

protractor --version || npm install -g [email protected]

but the one that will also check version of the package.

question from:https://stackoverflow.com/questions/30667239/is-it-possible-to-install-npm-package-only-if-it-has-not-been-already-installed

Answer 1

with bash you can do

[ $(node -p "require('protractor/package.json').version") != "2.1.0" ] && npm install [email protected]