Is there a way to check if a native Javascript function was monkey patched?

Question

For example I loaded a script on some website, and I would like to know if JSON.parse/stringify wasn't monkey patched.

I noticed that if I use toString on the function in Chrome/FF, JSON.stringify.toString, then I get back:

function stringify() {
    [native code]
}

My question is do you think this is a good way to verify if a function was monkey patched? Also would love to hear of any other approaches to this problem.

Answer 1

One could easily fake JSON.stringify.toString

JSON.stringify = function() {}
JSON.stringify.toString = function() {return 'ha-ha'}

console.log(JSON.stringify); //ha-ha

A little more robust way would be to use Function.prototype.toString

Function.prototype.toString.call(JSON.stringify)

But really bad monkeypatcher could patch Function.prototype.toString as well :)