socket.io unqiue变量

Question

io.sockets.on('connection', function (socket) {
      socket.on('something', function(data){
             var VAR1 = true;
             if(VAR1 === true){
             VAR1 = false;
             }
      });
});

Is the variable "VAR1" unique for every user who triggers the socket event "something"? Let's say that there are 1000 users will every connections to the socket event's variable start with VAR1 being true, and can others alter it? Is it unique to every connections?

Answer 1

Your VAR1 is unique for every single .on('something') event that occurs and will be lost as soon as the event handler is over. It is a local variable inside that event handler so a new VAR1 is created every single time the event handler is called and it will be garbage collected by Javascript as soon as the event handler has finished running. The next time the event handler is triggered, a new VAR1 will be created and then garbage collected.

Now, if you wanted it to be unique for each separate connection and last for the duration of that connection, you could declare it at a slightly different higher scope like this:

io.sockets.on('connection', function (socket) {
      var VAR1 = true;
      socket.on('something', function(data){
             if(VAR1 === true){
                 VAR1 = false;
             }
      });
});

Now, a new VAR1 will be created for each socket that connects and that variable will last for the duration of that connection (because it's in a closure) and each .on('something', ...) event that occurs will be able to access a unique VAR1 for each separate socket.

---

FYI, if you want a unique variable for a socket, you can also just add a property to the socket object iself:

io.sockets.on('connection', function (socket) {
      socket.VAR1 = true;
      socket.on('something', function(data){
             if(socket.VAR1 === true){
                 socket.VAR1 = false;
             }
      });
});