build.js

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

const serialize = require('./lib/serialize')
const hydrate = require('./lib/hydrate')

;(async (fileName) => {
  const browser = await puppeteer.launch()
  const page = await browser.newPage()

  page.on('console', event => console.log(event._text))

  page.on('load', async (...args) => {
    await page.$eval('body', serialize)
    const pageContent = await page.content()

    fs.writeFile(
      path.join(__dirname, fileName.replace('.html', '.ssr.html')),
      pageContent.replace('</body>', `${hydrate}</body>`),
      {encoding: 'utf8'},
      async (err) => {
          await browser.close();
      }
    )
  })

  await page.goto('file://' + path.join(__dirname, fileName))    
})('/public/index.html')