How do I get postcss-loader, postcss-cssnext and sass-loader to work together in webpack?

Question

This is my Webpack configs for scss/css files.

...
{
    test: /\.s?css$/,
    use: [
      'style-loader',
      { loader: 'css-loader', options: { importLoaders: 2 } },
      {
        loader: 'postcss-loader',
        options: {
          ident: 'postcss',
          plugins: loader => [
            require('postcss-import')({ root: loader.resourcePath }),
            require('cssnano')(),
            require('postcss-cssnext')(),
          ]
        }
      },
      'sass-loader',
    ]
}
...

The problem is that when I use cssnext functions like gray(100), the output CSS file has an empty value where the function was placed. I would like to know what I did wrong here.

i.e. background-color: gray(100); outputs to background-color: ;

I'm new to postcss so I don't really know how it works or how to configure it properly as of yet.

Answer 1

For your exact problem, the cssnext functions, you must put cssnano after postcss-cssnext, like below:

...
{
    test: /\.s?css$/,
    use: [
      'style-loader',
      { loader: 'css-loader', options: { importLoaders: 2 } },
      {
        loader: 'postcss-loader',
        options: {
          ident: 'postcss',
          plugins: loader => [
            require('postcss-import')({ root: loader.resourcePath }),
            require('postcss-cssnext')(),
            require('cssnano')(),
          ]
        }
      },
      'sass-loader',
    ]
}
...

BUT I don't know, why did you use sass-loader? when you have postcss in your project.

Actually PostCSS can do all jobs like sass even better, it is up to you for syntax style, I suggest see THIS REPO, it has complete configuration of PostCSS on Webpack, also in this repo, the SCSS syntax is used.

For clearness I write a part of configuration below:

rules: [
    {
        test: /\.(js|jsx)$/,
        exclude: /(node_modules\/)/,
        use: [
            {
                loader: 'babel-loader',
            }
        ]
    },
    {
        test: /\.pcss$/,
        use: ExtractTextPlugin.extract({
            fallback: 'style-loader',
            use: [
                {
                    loader: 'css-loader',
                    options: {
                        modules: true,
                        importLoaders: 1,
                        localIdentName: '[hash:base64:10]',
                        sourceMap: false,
                    }
                },
                {
                    loader: 'postcss-loader',
                    options: {
                        config: {
                            path: `${__dirname}/../postcss/postcss.config.js`,
                        }
                    }
                }
            ]
        })
    }
]

Even I use *.pcss instead of *.scss, *.sass or *.css, it is just for consistency and no different.

The PostCSS configuration is in separated file, it is:

module.exports = {
    ident: 'postcss',
    syntax: 'postcss-scss',
    map: {
        'inline': true,
    },
    plugins: {
        'postcss-partial-import': {
            'prefix': '_',
            'extension': '.pcss',
            'glob': false,
            'path': ['./../src/styles']
        },
        'postcss-nested-ancestors': {},
        'postcss-apply': {},
        'postcss-custom-properties': {},
        'postcss-nested': {},
        'postcss-cssnext': {
            'features': {
                'nesting': false
            },
            'warnForDuplicates': false
        },
        'postcss-extend': {},
        'css-mqpacker': {
            'sort': true
        },
        'autoprefixer': {
            'browsers': ['last 15 versions']
        },
    }
};

Absolutely cssnext works well, I used color() function and it works well.