事件未在socket.on（'connect'，event）上调用

Question

I'm having an issue with socket.io, at least I think, where a function in my client code is not being called on socket.on('connect', onsocketConnected);

However, if I put a conditional such as:

if(socket.connect) {
    onsocketConnected();
}  

Then my function gets called. Also I just realized if I write it like
socket.on('connect', onsocketConnected()); that my function gets called correctly. My question is, upon a connection from the client to a server, is connect a value that is automatically supplied to the client? Looking at the documentation at https://socket.io/docs/client-api/ it states it should work as socket.on(event, callback function) .
Are the parenthesis in the callback function always required for it to work? Because it seems like they are working elsewhere without parenthesis. Any resources or pointers to documentation is much appreciated.

Answer 1

In order to call a function (callback or whatever), while the function does not get any arguments, you should still call it with () . IE: onsocketConnected () ;

The reason socket.on('connect', onsocketConnected); didn't work is because you are missing () while calling for a function.
What you are doing by this, is just passing the variable/object (which does not exist) onsocketConnected to socket.on method, instead of passing a Function.

The right way to use it, is just as you typed afterwards: socket.on('connect', onsocketConnected());

Documentation about JS function arguments: http://devdocs.io/javascript/functions/arguments