Closure Question

[cations]

Hello I am learning JavaScript.

In regards to the below shim why did the author put var F outside of the anonymous function(o) and create a closure. Wouldn't var F inside of function(o) have worked also?

Thank you.

if (typeof Object.create != 'function') {
  (function () {
    // why is this outside of Object.Create.
	var F = function () {};
    Object.create = function (o) {
      if (arguments.length > 1) { throw Error('Second argument not supported');}
      if (o === null) { throw Error('Cannot set a null [[Prototype]]');}
      if (typeof o != 'object') { throw TypeError('Argument must be an object');}
      F.prototype = o;
      return new F;
    };
  })();
}

[Jeff Mott]

Probably to avoid it being recreated with every invocation. Better performance.

[handcraftedweb]

If F were declared in the Object.create function, a new version of F would be created each time Object.create is called. With F declared outside Object.create, the same F will be used each time Object.create is called.

The semantics (of F inside vs. outside) are technically different, but in practicality I don't see any difference, except as Jeff Mott mentioned the performance issue. Where'd you find this code?

[cations]

Probably to avoid it being recreated with every invocation. Better performance.

Ahh I see; by putting it outside it becomes a static variable of function (o).

So all variables outside of the inner function that forms the closure are static variables of that inner function. Correct?

Where'd you find this code?

http://stackoverflow.com/questions/3...roperty-in-es5

Thank you for the response.

[cations]

Does the below code produce the identical result as the originally posted code?

Thank you.

New Code:

if (typeof Object.create != 'function') {
  (function () {
	
	Object.create = function (o) {
		
		if (arguments.length > 1) { throw Error('Second argument not supported');}
		if (o === null) { throw Error('Cannot set a null [[Prototype]]');}
		if (typeof o != 'object') { throw TypeError('Argument must be an object');}
		
                //create a new object
	        var newObject = {};

		//set the newObject's prototype.
		newObject.prototype = o;	
		
		//return newObject
		return newObject;
	};
  })();
}

Original Code

if (typeof Object.create != 'function') {
  (function () {
    // why is this outside of Object.Create.
	var F = function () {};
    Object.create = function (o) {
      if (arguments.length > 1) { throw Error('Second argument not supported');}
      if (o === null) { throw Error('Cannot set a null [[Prototype]]');}
      if (typeof o != 'object') { throw TypeError('Argument must be an object');}
      F.prototype = o;
      return new F;
    };
  })();
}

[cations]

Please ignore the last question. I thought the prototype object was stored in the property prototype but I just learned it's stored in __proto__ which is now deprecated, hence the reason for the original code.