Socket io on the client side?

Question

JavaScript

There is an app on node+socket.io . Suppose the client has a js file containing a socket connection and the following message

socket.on('join', function(nickname) {
        socket.nickname = nickname;
        socket.broadcast.emit('notice', nickname + ' has joined the chat.');
      });

Questions:
1) How to make sure that the user cannot change the js code in his developer tool in the browser (I saw this on some sites)
2) Why if I forcefully write test instead of join in the developer tool, everything still works fine and performs what it was before the changes? Does it somehow cache the server-client interaction for itself? Or is it because these functions themselves are executed in document.ready and js itself caches this for itself?

Answer 1

1. Not at all
2. Because the code was already executed before it was changed.