How to use webpack's mode/variable in js code?

Question

webpack

The webpack.config is set to mode = 'development'
how can I use this variable in the code to display some debug messages depending on the mode, and ideally if the mode is 'production' so that this extra code does not exist at all.

Something like: if you write like this, then it writes undefined, but I can’t understand how to make this variable available in the code.
if (mode == 'development') console.log (mode);

Answer 1

// js (НЕ webpack.config.js)

console.log(process.env.NODE_ENV)

The environment variable process.env.NODE_ENVwill not work in the webpack config file, for webpack version 4.
Specify the environment