JSON.stringify fails on a newly created object (node, javascript)

Question

Ok, this one has to be a very easy question, but I just started learning node. I am also new to javascript, so, please show no mercy on pointing out wrong directions below.

In particular I have two files:

one has a class that creates some slave servers in different ports
the other one is the "main" file that generates the slaves

When I attempt to print out what I have just initialized I get two weird errors:

connections property is deprecated. Use getConnections() method, and then
it crashes when I attempt to apply JSON.stringify in the new object (Converting circular structure to JSON)

Code for slaves in file "slave.js":

var http = require ("http");

function Slave () {
}

Slave.prototype.ID           = undefined;
Slave.prototype.coordinator  = false;
Slave.prototype.httpServer   = undefined;
Slave.prototype.thePort      = undefined;

Slave.prototype.isCoordinator = function () { return this.coordinator; }

/*****************************************************************/

function handle_incoming_request (req, res) {
    console.log("INCOMING REQUEST: " + req.method + " " + req.url);
    res.writeHead (200, { "Content-Type" : "application/json" });
    res.end( JSON.stringify({ "error" : null }) + "\n" );
}

exports.createSlave = function (id, coordinatorK, port) {
    var temp         = new Slave ();
    temp.ID          = id;
    temp.coordinator = coordinatorK;
    temp.thePort     = port;
    temp.httpServer  = http.createServer(handle_incoming_request);
    temp.httpServer.listen (temp.thePort);
    console.log ("Slave (" + (temp.isCoordinator() ? "coordinator" : "regular") + ") with ID " + temp.ID + " is listening to port " + temp.thePort);
    console.log ("--------------------------------------------");

    return temp;
}

Now, the main file.

var http   = require ("http");
var url    = require ("url");
var a      = require ("./slave.js");

var i, temp;
var myArray = new Array ();

for (i = 0; i < 4; i++) {
    var newID = i + 1;
    var newPort = 8000 + i + 1;
    var coordinatorIndicator = false;

    if ((i % 4) == 0) {
        coordinatorIndicator = true; // Say, this is going to be a coordinator
    }

    temp = a.createSlave (newID, coordinatorIndicator, newPort);
    console.log ("New slave is  : " + temp);
    console.log ("Stringified is: " + JSON.stringify(temp));

    myArray.push(temp);
}

You can't stringify just any old object.

Pointy
– Pointy

2013-09-10 18:15:00 +00:00
Commented Sep 10, 2013 at 18:15 — Pointy
– Pointy, Commented Sep 10, 2013 at 18:15

user2736012 · Accepted Answer · 2013-09-10 18:35:59Z

3

You're trying to stringify the result of http.createServer(...). That'll not be what you want to do, so when you create that property, make it non-enumerable by defining it using Object.defineProperty().

exports.createSlave = function (id, coordinatorK, port) {
    var temp         = new Slave ();
    temp.ID          = id;
    temp.coordinator = coordinatorK;
    temp.thePort     = port;

    Object.defineProperty(temp, "httpServer", {
        value: http.createServer(handle_incoming_request),
        enumerable: false, // this is actually the default, so you could remove it
        configurable: true,
        writeable: true
    });
    temp.httpServer.listen (temp.thePort);
    return temp;
}

This way JSON.stringify won't reach that property curing its enumeration of the object.

edited Sep 10, 2013 at 18:35

answered Sep 10, 2013 at 18:19

user2736012

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2 Comments

MightyMouse Over a year ago

It is true that this one is working, with a minor change: the command temp.httpServer.listen (temp.thePort); should be after the Object.defineProperty(...). Please change this order. I will wait for a few more minutes to see if there is another answer before I accept it. Thank you for your time!

user2736012 Over a year ago

Sure, I changed it. Didn't notice the order when I was editing.

PSL · Accepted Answer · 2013-09-10 18:29:28Z

2

Issue is the with the property httpServer of temp object having circular reference. You can either set it non enumerable using Ecmascript5 property definision as mentioned in the previous answer or you can use the replacer function of JSON.stringify to customize it not to stringify the httpServer property.

   console.log ("Stringified is: " + JSON.stringify(temp, function(key, value){
         if(key === 'httpServer') return undefined;
        return value;
    }));

answered Sep 10, 2013 at 18:29

PSL

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2 Comments

MightyMouse Over a year ago

Thank you PSL for your time and the alternate explanation. I appreciate it. I am granting this one on user2736012 because he is lower on reputation though.

PSL Over a year ago

@MightyMouse You are welcome.. Ideally in node world you should go with EcmaScript5 definitions which will make it more standard way of defining objects. Since it was already posted i just provided an alternate.. You chose the right answer.. :)

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