Using local and global variables properly in node.js

Question

I am getting closer I think to understanding how global and local objects work in node.js but I am getting tripped up when it comes to something more complex like a server.

In my understanding in node.js a server is accessed by many but should only be instanced once so this confuses the hell out of me, I don't know how other servers behave (I'm using a web sockets server https://npmjs.org/package/ws)

I also understand:

var _global='global';
function testing(){
    var _local='local';
    console.log(_global+' & '+_local);// 'global & local'
    return;}
testing();
console.log(_global+' & '+_local);// 'global & undefined'

Now in node.js if I declared that _local var inside a server would that mean that it's a unique variable for each person?

If I create a global server:

var wss=new WebSocketServer({host:port});
wss.on('connection',function(soc){
    soc['uid']=Math.floor(Math.random()*101);
    console.dir(soc);
    });

navigate to the page that connects to the server, I see (on my putty ssh client) the websocket object with the attached id.

Then if a second user visits that page I see (in ssh) that the websocket object now looks like a new object no old id just a new one I don't see two connections...

So I was thinking

Should I make this socketserver local by putting it in a http.server and call the server with ajax?

client:

var xhr=XHRobject();
xhr.open("POST","mysite.com:8005",true);
xhr.setRequestHeader("Content-Type","text/csv");
xhr.send('create server');

server:

var http = require('http');
http.createServer(function(req,res){
    req.on('data',function(chunk){
        chunk=chunk.toString('utf8');
        if(chunk==='create server'){
            wss=new WebSocketServer({host:port});//etc..
            }
        });
    });

This would create a problem though I think as the WebSocketServer has a list wss.clients list of connected websockets that needs to be accessed so I don't think that I should have more than one server...?

If I declaire a variable (var localisedsocket) and put the wss.on('connection',function(soc){soc=localisedsocket;}); inside the http server, then would every user that opens the WebSocketServer no-longer be writing over the socket object?

Am I getting this theory right?

alex · Accepted Answer · 2014-01-31 20:03:12Z

2

Am I getting this theory right?

No. Your "_global" variable is just a local variable in the upper scope.

Anyway, the rule of thumb is: unless you have a good reason to do otherwise, always use local variables, and place "var" at the last possible moment (means, in the lowest scope possible).

answered Jan 31, 2014 at 20:03

alex

12.3k3 gold badges33 silver badges43 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

BENZ.404 Over a year ago

why place var as low as possible?

alex Over a year ago

In order to limit the scope of the variable, avoid unintended variable sharing and memory leaks.

BENZ.404 · Accepted Answer · 2014-02-01 04:12:10Z

1

No need for a http server or ajax. All that needs to be done is like this:

var wss=new WebSocketServer({host:port});//-----global for everyone
wss.on('connection',function(soc){
    var s={};//------------------------------s is local and unique to the user!
    s[1]=soc;
    s[1]=Math.floor(Math.random()*101);
    console.dir(s[1]);
    console.dir(wss);//-------now everyone can see all connected clients
    });

The point is that the server must be global but the socket must be local. Everyone is using the same server but when a user connects they get their very own WebSocket!

I think that finally I don't just see the difference between local and global but, I finally see the usefulness of this feature in javascript!

edited Feb 1, 2014 at 4:12

answered Jan 28, 2014 at 16:05

BENZ.404

5031 gold badge5 silver badges20 bronze badges

Collectives™ on Stack Overflow

Using local and global variables properly in node.js

2 Answers 2

2 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related