Why node.js requires an upgrade while trying to run an application on the localhost?

Question

When I try to run my node.js application on a localhost server, it does not run and demands a required upgrade. I have tried to run the code but I get the following error:

Answer 1

Do not open a client HTML file as a localhost URL but open the file directly.

After running your web-socket server,

localhost:[port]/client.html -> you will get the message "upgrade required".

file:///[folder]/client.html -> you can see your HTML file.

because you don't have any web-server with a web-socket or you did not configure your web server for your web-socket. So, you should use your file system.

The easiest way is to use right click on the client file and open it with your favorite browser.