Why doesn't web socket work with js?

Question

Flask

I'm trying to create a web socket using JS without wrappers and other things

new WebSocket("ws://www.example.com/socketserver");

but it can't even connect to the server, but if I use the Socket.IO library on the front, then everything connects fine.
On the back I have Flask-Socket.IO, can you explain to me why nothing works without wrappers on the front?