Wildcard Subdomain help needed

I want to dynamically create subdomain sites such as "user1.example.com", "user2.example.com" and serve static html and css based on subdomain. For a real world example blogger.com servers html and css for different users on blogspot domainl link https://althouse.blogspot.com/. I want to do exactly the same thing like blogger.com does.

Questions:

• What code do I need to write for determining subdomain (using js). For example user1.example.com the subdomain is user1.
• Should I store user html, css in s3 by creating folders such as user1/, user2/.

What you are trying to achieve cannot be done with S3 alone.

Assuming you have already created a Wildcard DNS record for your domain name, you will need to write some server-side code to achieve this. On your server, you will check for the Host header and accordingly serve the correct html page based on that.

Crude sample code for Node.Js + Express will look like:

if (req.host === chetan.blogspot.com) {
   return res.render("chetan.html");
} else if (req.host === jain.blogspot.com) {
   return res.render("jain.html");
}