What does it do when I run this command:
npm install --save-dev package1 package2
It is definitely not installing multiple packages, but it looks to be essential. (For example https://www.browsersync.io/docs/gulp)
For me it throws following ERRs:
Save as dependencies:
npm i package1 package2
Save as dev-dependencies:
npm i -D package1 package2
npm i --save-dev package1 package2