I am not too good with front-end technologies... So if I have wrong expectations - please correct me or my code. I have created a repository with code that allows to reproduce issue. Here is the link: https://github.com/ffatheranderson/webpack-issue-reproduction

as described in readme.md of the project:

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• What I expect? - I expect that after I execute npm run watch command - the generated result/bundle.js file to have such lines:

...
var _environment = 'development';
var _ANOTHER_VARIABLE = "another variable value";
...

• What is actual result? - after I execute npm run watch command - the generated result/bundle.js file contains such lines:

...
var _environment = undefined;
var _ANOTHER_VARIABLE = "another variable value";
...

• Why do I have such expectations? - because of these lines:

...
  plugins: [
        new webpack.DefinePlugin({
            ENVIRONMENT: JSON.stringify(process.env.NODE_ENV),
            ANOTHER_VARIABLE: JSON.stringify("another variable value"),
        })
    ]
...

in webpack.config.js file.

As you can see variable _environment is not initialized with development value as it is promised here: https://webpack.js.org/configuration/mode/

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