How can I use variables in package.json?

Any property from package.json can be referenced from scripts, prefix it with $npm_package and adding an _<prop> (underscore + property) for every nested level.

Example:

{ 
  "name": "appname",
  "version": "0.0.1"
}

Here, name can be access like below:

Linux/Mac: $npm_package_name or ${npm_package_name}

Windows: %npm_package_name%

And, version can be access like below:

Linux/Mac: $npm_package_version or ${npm_package_version}

Windows: %npm_package_version%