The following code comes from an academic example, its intention is to load a page that exists in the file system:

const sendErrorResponse = res => {
    res.writeHead(httpStatus.NOT_FOUND, {"Content-Type": "text/html"});
    res.write("<h1>FILE NOT FOUND</h1>");
    res.end();
};

const customReadFile = (file_path, res) => {
    if (fs.existsSync(file_path)){
        fs.readFile(file_path, (error, data) => {
            if (error) {
                sendErrorResponse(res);
                return;
            }
            res.write(data);
            res.end;
        })
    } else {
        sendErrorResponse(res)
    }
};

const port = 3000,
    http = require("http"),
    httpStatus = require("http-status-codes"),
    fs = require("fs");

http.createServer((req, res)=> {
    let url = req.url;
    console.log(`Requested url: ${url}`);
    if (url.indexOf(".html") !== -1) {
        res.writeHead(httpStatus.OK, {"Content-Type": "text/html"});
        customReadFile(`./views${url}`, res);
      } else if (url.indexOf(".js") !== -1) {
        res.writeHead(httpStatus.OK, {"Content-Type": "text/javascript"});
        customReadFile(`./public/js${url}`, res);
      } else if (url.indexOf(".css") !== -1) {
        res.writeHead(httpStatus.OK, {"Content-Type": "text/css"});
        customReadFile(`./public/css${url}`, res);
      } else if (url.indexOf(".png") !== -1) {
        res.writeHead(httpStatus.OK, {"Content-Type": "image/png"});
        customReadFile(`./public/images${url}`, res);
      } else {
        sendErrorResponse(res);
      }
})
.listen(port);

console.log(`The server has started and is listening on port: ${port}`);

The issue is that when rendered the page in the browser (chrome), the loading icon in the tab keeps refreshing like waiting for a resource.

Can you tell me, what is causing this?