How do i use a variable in my webpack.config file?

I am using webpack 2.2.1.

I want to define a variable on the command line, then use that variable in my build config.

So give a webpack command line that looks something like (or whatever it needs to be):

webpack "--output-path=..." "--env.wibble=NOMF"

How can I then write something like:

... 

const config = {
  entry: {
    ...
  },
  output: {
    ...
  },

  plugins: [
    ...
    new CopyWebpackPlugin([{
      from: '/somepath/' + env.wibble,
      to: 'something.js'
    }]),    
    ...
  ],

};

module.exports = config;

How can I define and use a variable in my build?

I'm intentionally not using NODE_ENV here (if I can).

Solution

The --env option is used to pass the defined properties to the webpack config, but for this to work you need to export a function that returns the configuration object, not the object itself.

Your config would be:

module.exports = function(env) {
  const config = {
    entry: {
      // ...
    },
    output: {
      // ...
    },
    plugins: [
      new CopyWebpackPlugin([{
        from: '/somepath/' + env.wibble,
        to: 'something.js'
      }]),    
    ],
  };
  return config;
};

You can shorten it by using an arrow function to implicitly return the object:

module.exports = env => ({
  entry: {
    // ...
  },
  output: {
    // ...
  },
  plugins: [
    new CopyWebpackPlugin([{
      from: '/somepath/' + env.wibble,
      to: 'something.js'
    }]),    
  ],
});