Node.js app to generate a thumbnail of the given URL

package.json

{
  "name": "web-thumbnails",
  "version": "1.0.0",
  "engines": {
    "node": "^8.4.0"
  },
  "description": "Generate thumbnails of web pages",
  "main": "server.js",
  "scripts": {
    "start": "node server.js",
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "steren@google.com",
  "license": "ISC",
  "dependencies": {
    "express": "^4.15.4",
    "puppeteer": "^0.10.2"
  }
}

server.js

const puppeteer = require('puppeteer');
const express = require('express');
const app = express();

app.use(async (req, res) => {
  if(req.path === '/') {res.end('Please provide URL');}

  const url = req.path.slice(1);
  console.log(`URL: ${url}`);

  const browser = await puppeteer.launch();
  const page = await browser.newPage();
  await page.goto(url);
  let imageBuffer = await page.screenshot();
  await browser.close();

  res.set('Content-Type', 'image/png')
  res.end(imageBuffer);
})

const server = app.listen(process.env.PORT || 3000, err => {
  if (err) return console.error(err);
  const port = server.address().port;
  console.log(`App listening on port ${port}`);
});