Cannot create Object of function defined in closure?

Question

Why is it that I can't create an object from a function defined in a closure?

var outer = function() {
  var constructor = function() { 
    this.foo = 1; 
  }; 
  return constructor;
};

// Should be: { foo: 1 }, but is: undefined
var constructorObject = new outer()();

// This works
var c = outer();
var constructorObject = new c();

function doesn't return anything and sets foo on the context object... try this: var ctxt = {}; new outer().call(ctxt); console.log(ctxt.foo); — gp.
– gp., Commented Oct 10, 2014 at 15:47

antyrat · Accepted Answer · 2014-10-10 15:46:01Z

3

Because by calling ()() you get the inner function result. And as inner function doesn't have return statement it equals to undefined.

If you want to return object there your function should be like:

var inner = function() {
    return { foo: 1 };
}

answered Oct 10, 2014 at 15:46

antyrat

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4 Comments

tonekk Over a year ago

I think the example is a bit misleading. I don't just want to nest functions, I want to return a constructor.

sma Over a year ago

Further, if you want to create another new object, then break them up into separate lines: var outerObj = new outer(); var inner = new outerObj(); console.log(inner);

antyrat Over a year ago

@tonekk so what do you expect to have in return? Object or constructor? Or what?

antyrat Over a year ago

you can try to return return this; then constructorObject.foo will equal 1. This is what you want?

MrCode · Accepted Answer · 2014-10-10 15:56:38Z

1

You need to wrap the outer function call in parenthesis like so:

var constructorObject = new (outer())();
//                          ^       ^ parenthesis here

console.log(constructorObject); // constructor {foo: 1} 
console.log(constructorObject.foo); // 1

answered Oct 10, 2014 at 15:56

MrCode

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1 Comment

tonekk Over a year ago

Ah I get it! The new is applied to 'outer' instead of the return of 'outer' (which is 'constructor'). Tricky :)

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