just take the development environment as an example

I saw this line of code in webpack.dev.conf.js,

new webpack.DefinePlugin({
      "process.env": require("../config/dev.env")
    }),

if I have this line of code, I can get the content configured in config/dev.env.js in vue.

if I comment out this line of code, I get process.env as a {} empty object,

but shouldn"t process.env in node be an environment variable in the system

process  Node.js   require()

since I commented out that line of code, it means I didn"t overwrite its value, so why did I get an empty object instead of the environment variable in the current operating system?