How to create instances of a global javascript namespace?

Question

I am a C++/Java developer that has been tasked with a javascript project and I cannot seem to figure this issue out.

I am working with a javascript file that defines a namespace by direct assignment as described here

So here is my attempt at an overly simplified example namespace

// testns.js
var ns = { }
ns.val = -1;

ns.setVal = function(newVal) {
    this.val = newVal;
}

And here is what I would like to do

//myScript.js
function testNamespaceInstances()
{
    var nsInstance1 = ns;
    nsInstance1.setVal(1);

    var nsInstance2 = ns;
    nsInstance2.setVal(2);

    console.log("nsInstance1.val: " + nsInstance1.val);
    console.log("nsInstance2.val: " + nsInstance2.val);
}

That function will output

nsInstance1.val: 2
nsInstance2.val: 2

Is there anything I can do without modifying the testns.js file that the namespace is declared in so that the function will output

nsInstance1.val: 1
nsInstance2.val: 2

Edit: Added some more details to the example code. I would also like to note I am attempting to simplify a more complex javascript file that I am working with

Steve Wang · Accepted Answer · 2012-07-24 20:15:47Z

3

Just create a second namespace (object, really): nsInstance2 = {}; -- the problem here is that both nsInstance1 and nsInstance2 are pointing to the same object, so naturally, if you change the properties of one, it'll be reflected in the other.

answered Jul 24, 2012 at 20:15

Steve Wang

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Comments

Mitya · Accepted Answer · 2012-07-24 20:54:47Z

3

Complex data types in JavaScript are copied as references, so your nsInstance1 and nsInstance2 variables merely point to the namespace object - they do not copy or instantiate it.

To instantiate it, the namespace must be declared as a function, not an object literal, and referenced with the new keyword. Only functions can be used in instantiation in JavaScript.

function NS() {}
var ns1 = new NS();
var ns2 = new NS();

edited Jul 24, 2012 at 20:54

answered Jul 24, 2012 at 20:16

Mitya

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4 Comments

snctln Over a year ago

Thanks for the answer, I agree that this is the way to go, unfortunately I am trying to accomplish this without modifying the contents of the nstest.js file.

Mitya Over a year ago

You're welcome. In that case, you're going to have to re-think things because object literals cannot be instantiated.

katspaugh Over a year ago

@Utkanos, what about Object.create?

Mitya Over a year ago

@katspaugh - sure, worth a mention, but I don't tend to suggest it as I assume OPs need support for IE <= 8.

j08691 · Accepted Answer · 2012-07-24 20:17:35Z

1

You could do the following:

var ns = function() {
    return {};
};

and

function testNamespaceInstances() {
    var nsInstance1 = new ns;
    nsInstance1.val = 1;

    var nsInstance2 = new ns;
    nsInstance2.val = 2;

    console.log("nsInstance1.val: " + nsInstance1.val);
    console.log("nsInstance2.val: " + nsInstance2.val);
}

jsFiddle example

answered Jul 24, 2012 at 20:17

j08691

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Comments

katspaugh · Accepted Answer · 2012-07-24 21:16:36Z

1

First, there are no namespaces in JavaScript. {} is just an object literal, the same as new Object().

Second, you don't instantiate objects by giving them several references. You can instantiate an object with Object.create:

var nsInstance1 = Object.create(ns);
var nsInstance2 = Object.create(ns);

edited Jul 24, 2012 at 21:16

answered Jul 24, 2012 at 20:16

katspaugh

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3 Comments

michaelok Over a year ago

No namespaces in JavaScript? "Namespaces can be found in almost any serious JavaScript application."

katspaugh Over a year ago

@michaelok, whenever you have to type a dot before a symbol – it's not a namespace but a fake. We need portable scope, like import * from module in Python.

michaelok Over a year ago

Good point, thanks for the explanation. This article and the post by Kevin Dangoor also clarified the issue "JavaScript needs a standard way to include other modules and for those modules to live in discreet namespaces. There are easy ways to do namespaces, but there’s no standard programmatic way to load a module (once!)."

Victor Ribeiro da Silva Eloy · Accepted Answer · 2012-07-24 20:19:18Z

0

//myScript.js
Object.prototype.clone = function() {
  var newObj = (this instanceof Array) ? [] : {};
  for (var i in this) {
    if (i == 'clone') continue;
    if (this[i] && typeof this[i] == "object") {
      newObj[i] = this[i].clone();
    } else newObj[i] = this[i]
  } return newObj;
};

function testNamespaceInstances()
{
    var nsInstance1 = ns.clone();
    nsInstance1.val = 1;

    var nsInstance2 = ns.clone();
    nsInstance2.val = 2;

    console.log("nsInstance1.val: " + nsInstance1.val);
    console.log("nsInstance2.val: " + nsInstance2.val);
}

answered Jul 24, 2012 at 20:19

Victor Ribeiro da Silva Eloy

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Comments

spaceman12 · Accepted Answer · 2012-07-24 20:27:16Z

0

Since your are taking ns at a global scope, you can just directly assign values to it like-

//testns.js



var ns = { }
ns.val = -1;

function testNamespaceInstances()
{
    ns.val1=1;
    ns.val2=2;

    console.log("ns.val1: " + ns.val1);
    console.log("ns.val2: " + ns.val2);
}

answered Jul 24, 2012 at 20:27

spaceman12

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