The platform independent way to provide environment variables inside “npm scripts” section

index.js

const ENV = process.env.NODE_ENV;

package.json

{
  "name": "run-scripts",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "start": "webpack",
    "build:release": "cross-env NODE_ENV=production webpack",
    "build:debug": "cross-env NODE_ENV=development webpack"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "dependencies": {
    "cross-env": "^4.0.0",
    "webpack": "^2.3.3"
  }
}

webpack.config.js

const webpack = require('webpack');

module.exports = {
  entry: {
    main: './index.js'
  },

  output: {
    path: __dirname + '/public',
    filename: '[name].js'
  },

  plugins: [
    new webpack.DefinePlugin({
      'process.env.NODE_ENV': JSON.stringify(process.env.NODE_ENV),
    })
  ]
};