Create a single object

Question

I want to create a single object. Does the below code make sense?

singleObj = new function () {
    // act as a constructor.
};

Am I hurting any good practice?

I need a constructor. A simple object literal would not be useful here.

maybe duplicate question: http://stackoverflow.com/questions/1479319/simplest-cleanest-way-to-implement-singleton-in-javascript — Andreas Köberle, Aug 12 '11 at 16:59
Why do you think you need a constructor *without* a custom prototype? — katspaugh, Aug 12 '11 at 17:02
I don't think this is a duplicate. The OP is invoking the `new` operator on an anonymous function. I don't think I've ever seen that before and I've been writing JavaScript for at least 13 years. It _is_ legal JavaScript, however.... — Ray Toal, Aug 12 '11 at 17:02
*Why* wouldn't an object literal be useful there? It seems like a text-book case to *moi*. — Michael Lorton, Aug 12 '11 at 17:03
@katspaugh -- if that's the case, he needs the [module](http://yuiblog.com/blog/2007/06/12/module-pattern/) pattern, not to screw around with the `new` operator. — Michael Lorton, Aug 12 '11 at 17:08
@thom -- I know your response feels explanatory to you, but from the outside it is just circular. *Why* do you need a constructor, especially for a singleton? — Michael Lorton, Aug 12 '11 at 17:09
I want to register some events in constructor. Thank you Malvolio. — thom, Aug 12 '11 at 17:17
@thom: You ought to stop repeating that. Stating that you "need" the thing that you've decided is going to be your implementation does not help us to understand _why_ you've decided that. "Why do you need a constructor?" "Because I need a constructor" — Lightness Races in Orbit, Aug 12 '11 at 18:02

score 1 · Answer 1 · edited Aug 12 '11 at 17:02

1

If you want just a single object, in that you are never going to make one again, an object literal works perfectly here.

var x = { };

Will give you an object. In order for

var F = function() {
};

to give you an object you will need to invoke F

var x = new F();

edited Aug 12 '11 at 17:02

Michael Lorton

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answered Aug 12 '11 at 17:01

zellio

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score 0 · Answer 2 · answered Aug 12 '11 at 17:01

0

you could try someting like:

var objCreate = function() {
    var obj = {};
    // do constructor logic
    return obj;
};

answered Aug 12 '11 at 17:01

Warspawn

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score 0 · Answer 3 · answered Aug 12 '11 at 17:02

0

Just create a new object and then populate it. You don't need a contrustor to do this.

var singleObject = {};
singleObject.value1 = "whatever";

If you really want to use a function, then you need to actually call it.

var singleObj = new (function () {
    // act as a constructor.
})();

We can use a self executing function by creating a anonymous function function(){}, and immediately calling it with an empty argument set.

answered Aug 12 '11 at 17:02

Paul Perigny

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And it's not self-executing, unless it's a function cutting it's own head. – katspaugh Aug 12 '11 at 17:06
When `new` "calls" the function directly you can't pass in arguments. The form I suggested will allow it. If you don't need to parametrize your constructor then there no point in calling either call forms. – Paul Perigny Aug 12 '11 at 17:08
Self-executing functions are commonly used to control name space pollution by creating new namespaces (closure). In essence they are used to create a set of variables that disappear at the end of a function. (ie they commit suicide.) – Paul Perigny Aug 12 '11 at 17:18
Local variables commit suicide upon any function's returning, so it's not a valid explanation for the term "self-executing". – katspaugh Aug 12 '11 at 17:24

score 0 · Answer 4 · answered Aug 12 '11 at 17:02

http://www.w3schools.com/js/js_objects.asp

//Used to create an object
personObj=new Object();
personObj.firstname="John";
personObj.lastname="Doe";
personObj.age=50;
personObj.eyecolor="blue";

//Used as a constructor for the object
function person(firstname,lastname,age,eyecolor)
{
this.firstname=firstname;
this.lastname=lastname;
this.age=age;
this.eyecolor=eyecolor;
}
//how to declare objects via constructor template
var myFather=new person("John","Doe",50,"blue");
var myMother=new person("Sally","Rally",48,"green");

Create a single object

4 Answers4