Install latest version of packages with npm

It seems if I use npm install --save <package_name>, it installs the latest stable version.

I want to install the absolutely latest release. So if I, for instance, want to install Bootstrap v4, I need to do npm install bootstrap@4.0.0-alpha.6 instead of just npm install bootstrap.

But if I didn't know that the latest version is named 4.0.0-alpha.6, I wouldn't be able to install it. Is there a flag or something else I can use to make sure I get the latest version?

via Jamgreen