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 inst

Answer 1

Function version of the excellent answer by @JeromeWAGNER:

function install_package_if_needed() {
    local p=${1:-Package required}
    local v=${2:-Version required}
    shift 2
    local i=$(node -p "require('$p/package.json').version" 2>/dev/null)
    [ "$i" == "$v" ] || npm "$@" install "$p@$v"
}

Use like:

$ install_package_if_needed protractor 2.1.0

To pass additional options to npm, specify them after the version, like so:

$ install_package_if_needed protractor 2.1.0 -g