middleware.js

import detector from "spider-detector";
import url from "url";

app.use(detector.middleware());

app.get("*", function(req, res, next) {

    //we only serve static snapshots to spiders
    if(!req.isSpider() ) {
        next();
        return;
    }
  
    let path = url.parse(req.originalUrl).pathname;
    
    if(path = "/")
      path = "/index";
  
    //if the files are in the cache folder:
    res.sendFile(`./cache/${path}.html`);
});