Calling toString on function proxy throws TypeError exception

[Boris Zbarsky]

On 10/27/15 4:35 AM, Claude Pache wrote:
> it is that, for any callable object, it will return a string and not throw, because it was so since the dawn of JS.

It's totally false for random "host objects" with a [[Call]] in ES5, per 
spec and in at least some implementations.  As you can tell in Firefox 
for example:

   Function.prototype.toString.call(document.createElement("object"))

(though it does not throw for document.all in Firefox, for interesting 
implementation reasons).

> That function will work (in the sense of: will return an answer; I'm not judging the quality of that answer) with anything reasonable fed to it (where "reasonable" excludes things like `(class { static toString() { throw "pwnd!" }})`).

Won't work with an HTMLObjectElement in at least some browsers.  How 
"reasonable" that is, who knows.

-Boris