Why is the JSON.stringify() replacer function not working?

Question

I have the following code:

http://jsfiddle.net/8tAyu/7/

var foo = {
    "foundation": "Mozilla",
    "model": "box",
    "week": 45,
    "transport": {
        "week": 3
    },
    "month": 7
};

console.log(JSON.stringify(foo, 
                           function(k, v) { 
                               if (k === "week") 
                                   return v;
                               else 
                                   return undefined;
                           }));

so supposedly, I thought at least the "week" that isn't nested should come back, and I will see how to make the nested one come back too. But no matter how I change it, the console.log prints out undefined, unless if I change the function simply to return v always, then I get back the whole object. Why is that?

Answer 1

Stringify seems to be called, first, with an empty 'k' for the root of the object. We return undefined for that, and all processing stops.

If we change it to:

if (!k || (k == "week") )

then the result is:

{"week":45}

You won't get the nested one, since we return undefined for "transport" and ignore all its contents.