npm install multiple package names

Question

What does it do when I run this command:

npm install --save-dev package1 package2

It is definitely not installing multiple packages, but it

Answer 1

It is definitely not installing multiple packages

Why? You're installing package1 and package2 and marking them as devDependencies with --save-dev.

As stated in the documentation, you may combine multiple arguments, and even multiple types of arguments. In your case, you're combining 2 package names published on the registry.