Universal server rendering

universal.js

const path = require('path');
const fs = require('fs');

const React = require('react');
const { renderToString } = require('react-dom/server');
const { StaticRouter } = require('react-router-dom');
const { ServerStyleSheet } = require('styled-components');

const { default: App } = require('../src/containers/App');

const indexFile = fs.readFileSync(path.resolve(__dirname, '..', 'build', 'index.html'), 'utf8');

global.window = undefined;
global.document = undefined;

module.exports = function universalLoader(req, res) {
    const css = new ServerStyleSheet();
    const context = {};

    // Create the markup from the React application
    const markup = renderToString(
        css.collectStyles(
            <StaticRouter context={context} location={req.url}>
                <App />
            </StaticRouter>
        )
    );

    if (context.url) {
        return res.redirect(context.url);
    }
    console.log(indexFile);
    const html = indexFile
        .replace('{{SSR}}', markup)
        .replace('{{CSS}}', css.getStyleTags());

    res.send(html);
};