I've managed to instrument functions in Javascript by creating another function, adding my own functionality to it and then invoking apply(this, arguments) :
window["functionA"] = function(){...}
On Google Chrome I also managed to instrument function setItem which belongs to localStorage so instead I wrote:
localStorage["setItem"] = function(){...}
The above works brilliantly, writing localStorage.setItem instead of localStorage["setItem"] also works.
Although this works on Google Chrome, on Firefox localStorage["setItem"] or localStorage.setItem are treated as stored items in localStorage instead of new functions, so whenever localStorage["setItem"] = function(){...} is invoked, function() {...} is stored as a String in location setItem in localStorage. Does anybody have any idea why Firefox treats this differently than Chrome or if there exists any sort of work around to this problem?
Have you tried patching the prototype of Storage instead?
Storage.prototype.setItem = function(key, value)
{
//
}