Transform CSS files use PostCSS

browserify-postcss.js

var through = require('through2');
var postcss = require('postcss');

function postcssTransform(filename, options) {
    if (!/\.css$/.test(filename)) {
        return through();
    }
    
    if (typeof options === 'undefined' || options === null) {
        options = {};
    }
    var processors = Array.isArray(options.processors) ? options.processors : [];

    var chunks = [];
    function transform(chunk, enc, next) {
        chunks.push(chunk);
        next();
    }

    function flush(callback) {
        var stream = this;
        var source = Buffer.concat(chunks).toString();

        postcss(processors)
            .process(source, { from: filename })
            .then(function (result) {
                var moduleBody = 'module.exports = ' + JSON.stringify(result.css) + ';';
                stream.push(moduleBody);
                callback();
            }, function (err) {
                callback(err);
            });
    }

    return through(transform, flush);
}

// Usage

browserify('path/to/app.js')
    .transform(postcssTransform, {
        processors: [
            url({ url: 'inline' }),
            cssnano({ safe: true })
        ]
    })
    .bundle();