When is a javascript function not an object?

Question

I'm seeing the following behaviour, in the middle of a javascript debug session:

o // function (a1, a2, a3) {  return a1 + a2 + a3; }

typeof(o) //'function'

for (var n in o) { console.log(n); } //<a list of properties>

Object.keys(o) //TypeError: not an object

Object.prototype.toString.call(o); //"[object Function]"

which makes me wonder - can a function, ever not be object?

[running on Chrome 29, on a mac]

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Note that this is in the middle of a very complex debug session. I don't exactly know where 'o' is coming from, or how it was created. Also, I've so far been unable to reproduce this issue with a simple test case. A simple setup works as expected:

var t = function() { return true; } //undefined
t.a = "aa" //"aa"
Object.keys(t) //["a"]

Answer 1

When you see something like this, you might try:

console.log(Object.keys)

or equivalent.

(if you can find the original implementation of keys for your browser, to compare and make sure it's identical to what you're seeing)

(read the comments on the question for more ideas of things to look at if seeing this kind of problem)

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False alarm. Functions are always objects, and the people at Chrome know how to make virtual machines.

I ran

grep -r "Object.defineProperty(" *

grep -r "Object.defineProperties(" *

and found a place where Object.keys is being overwritten, with a buggy function.

The related code was being loaded dynamically, so I didn't get to see it explicitly get loaded in the browser.