As of 0.8.3 webpackMerge mutates the inputs

[sullivanpt]

This is a new behavior that didn't occur in 0.7.x; I'm not sure its a "bug" but it should at least be documented. The webpackMerge function mutates the inputs, as evidenced by the unit test below. It's a problem because I've been using webpackMerge in series to build multiple distinct configurations, for example in webpack.config.js:

module.exports = [
  webpackMerge({}, defaultConfig, commonConfig, clientConfig),
  webpackMerge({}, defaultConfig, commonConfig, serverConfig)
]

The failing test:

  it('should not mutate inputs', function () {
    const a = {
      output: {
        filename: 'bundle.js'
      }
    };
    const b = {
      output: {
        path: 'path/b'
      }
    };

    const aClone = JSON.parse(JSON.stringify(a));
    merge({}, a, b);

    assert.deepEqual(a, aClone); // this fails with actual: -    "path": "path/b"
  });

[PatrickJS]

I use webpack-merge everywhere now but this is becoming a problem for universal applications

[bebraw]

Thanks for reporting! I was missing a little corner case there. Fixed in 0.8.4.

[PatrickJS]

thanks!