On Jul 14, 3:03 pm, xavierm02 <[email protected]> wrote:
> Hi,
>
> http://jsbin.com/ejodoq/edit
> http://jsbin.com/uqoyep/edit
> http://jsbin.com/opinus/edit
> http://jsbin.com/ejufih/edit
>I thought setting the prototype of a constructor was just like cycling
>through instances and change their __proto__...
The __proto__ is set to the Func.prototype at the time of new Func().
When you change Func.prototype to be some other object there's nothing
the "instances" can do about it.
It's not different than:
var A = {};
var b = {linkToA: A};
A = {id: 1};
Just because A points to a different object now, it doesn't make
b.linkToA to point to that same object too.
So when the .prototype of a function is assigned to another object
it's not going to affect the prototype chain of any object, unlike
changing the __proto__.
Here's a modified version of your code isolating the issue with only
one function: http://jsbin.com/ecufiz/3/edit
>I was wondering why it would silently fail in the first case and throw an
>error in all the others...
It's not failing like the others because there's no cycle on the
prototype chain.
"A.prototype instanceof B" checks B.prototype against each object of
"A.prototype" prototype chain. Since you've changed B.prototype to
something else it will never be found in the chain, hence returning
false.
Hope it's not confusing, It would be easier to explain with a
drawing..
Here's some more info:
13.2.2 [[Construct]] http://bclary.com/2004/11/07/#a-13.2.2
15.3.5.3 [[HasInstance]](V) http://bclary.com/2004/11/07/#a-15.3.5.3
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