webpack-plugin.js

function () {
    this.plugin("done", function (stats) {
        var replaceInFile = function (filePath, toReplace, replacement) {
            var replacer = function (match) {
                console.log('Replacing in %s: %s => %s', filePath, match, replacement);
                return replacement
            };
            var str = fs.readFileSync(filePath, 'utf8');
            var out = str.replace(new RegExp(toReplace, 'g'), replacer);
            fs.writeFileSync(filePath, out);
        };

        var hash = stats.hash; // Build's hash, found in `stats` since build lifecycle is done.

        replaceInFile(path.join(__dirname, '..', 'app', 'pages', 'assets.js'),
            'main.[^.]*.css',
            `main.${hash}.css`
        );
    });
}