Can you name an instance the same as its constructor name?

Question

var myFunc = new function myFunc(){};

?

As it seems, this replaces the Function Object with the new instance... which means this is a good Singleton.

I haven't seen anyone using this, so I guess, there are downsides to this that I am unaware of...

Any thoughts?

@PeeHaa埽 If you're not a JS guy, it doesn't matter if it looks strange to you as much... If it looked weird to a JS developer, then I would care more — Ruan Mendes, Apr 16 '13 at 18:02
What's the point of the second `myFunc` there? You can just as easily create a single instance of a class by saying `var myFunc = new function() { ... }`. — Joe Enos, Apr 16 '13 at 18:03
The lesson being my assumption is correct that it indeed does look strange? — PeeHaa, Apr 16 '13 at 18:03
@PeeHaa埽 I did miss the fact that the constructor was defined inline, that doesn't make a lot of sense, I concur — Ruan Mendes, Apr 16 '13 at 18:04
It could be implemented as funciton myFunc(){} var myFunc = new myFunc(). the idea id to create a singleton. and is this a good implantation of one. — user2071276, Apr 16 '13 at 18:08
Well... you could implement a lot of things in javascript. Doesn't make it a good idea ;) — PeeHaa, Apr 16 '13 at 18:09
@PeeHaa埽 I'm curious: Would you still find it weird if the function wasn't named? `var myFunc = new function() {...}` — Ruan Mendes, Apr 16 '13 at 18:37
Not really. That makes sense to me (syntax wise)`. Still don't see why on earth you want to do that though. — PeeHaa, Apr 16 '13 at 18:38
@PeeHaa埽 I do agree, sorry about the misunderstanding earlier, you helped me improve my answer a lot! — Ruan Mendes, Apr 16 '13 at 18:41

score 1 · Accepted Answer · edited May 23 '17 at 11:43

1

YES...

However, it does look weird that you're creating a named function but never refer to it by name.

The more common pattern(s) I've seen are

function MyClass(){
    this.val = 5;
};
MyClass.prototype.getValue = function() {
    return this.val;
}
MyClass = new MyClass();

But when people do that I wonder why they don't just use a literal object

var MyClass = {
    val: 5,
    getValue: function() {
        return this.val;
    }
}

And I would even prefer to use the module pattern here

var MyClass = (function(){
    var val = 5;
    return {
        getValue: function() {
            return val;
        }
    };     
})();

Disclaimer

Now whether the singleton pattern should be used, that's another question (to which the answer is NO if you care about testing, dependency management, maintainability, readability)

edited May 23 '17 at 11:43

Community

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answered Apr 16 '13 at 18:01

Ruan Mendes

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What is the use of `new function`? – PeeHaa Apr 16 '13 at 18:02
I didn't notice that part, that is surely a bit weird, let me fix the answer – Ruan Mendes Apr 16 '13 at 18:02
If you try to overwrite MyClass->val after "MyClass = new MyClass()" what happens? – Kris Georgiev Apr 16 '13 at 18:17
@KrisGeorgiev In all but the last case, you are overwriting the `val` property of `MyClass` (the object, not the class that is not the cosntructor that is notreachable anymore). In the last example, it's creating a new property on the object. I'm not sure what the point of your question is... – Ruan Mendes Apr 16 '13 at 18:22

score 0 · Answer 2 · answered Apr 16 '13 at 18:09

0

As it seems, this replaces the Function Object with the new instance

No, it does not replace anything. The name of a function expression (that's what you have) is only accessible inside the function itself, not outside of it. It would be exactly the same as if you omit the name:

 var myFunc = new function(){};

In general, if you don't want certain symbols accessible, just don't make them global. Define those symbols inside a function and just return whatever you want to make accessible, e.g:

var myobj = (function() {
    function Foo() {};
    // do whatever
    return new Foo();
}());

However, if you just want to create a single object, it is often easier to use an object literal:

var myobj = {};

There is no reason to use a constructor function if you only want to create a single instance from it. If you want to establish inheritance, you can use Object.create ^[MDN]

answered Apr 16 '13 at 18:09

Felix Kling

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Obviously this could be possible, but for readability reasons, you do not want to declare the instance the same place as the constructor this might be a good way to go about it... – user2071276 Apr 16 '13 at 18:14
The variable does shadow the named function, doesn't it? – Ruan Mendes Apr 16 '13 at 18:15
@Juan: As I said, a named function expression does not create a symbol with that name in the enclosing scope. The name is only available inside the function. Try `var foo = function bar() {}; alert(bar);`. – Felix Kling Apr 16 '13 at 18:17
I mean an example like what the OP has... where the variable and function names are the same. Something like `(function() { console.log("Before", MyFun); var MyFun = new function MyFun() {}; console.log("After", MyFun); })()`, the output is `Before undefined` followed by `After MyFun {} ` http://jsfiddle.net/WWLJ7/ – Ruan Mendes Apr 16 '13 at 18:28
@Juan: http://jsfiddle.net/WWLJ7/1/ ... the name of the function is not available in the enclosing scope. The function object will never be assigned to `MyFun` at any point. – Felix Kling Apr 16 '13 at 18:37
@FelixKling But in your example, you're not creating a name conflict ("where the variable and function names are the same"), which would create the "shadowing". I guess I don't understand what you're saying... – Ruan Mendes Apr 16 '13 at 18:39
@Juan: By choosing two different names `A` (variable) and `B` (function), I can show that there never is a conflict or shadowing because symbol `B` will never be created. The name you give to the function is completely irrelevant. – Felix Kling Apr 16 '13 at 18:40

Can you name an instance the same as its constructor name?

2 Answers2