Overriding XMLHttpRequest.open()

Question

How would I be able to override the XMLHttpRequest.open() method and then catch and alter it's arguments?

I've already tried the proxy method but it didn't work, although removing the open over-rid when XMLHttpRequest() was called:

(function() {
    var proxied = window.XMLHttpRequest.open;
    window.XMLHttpRequest.open = function() {
        $('.log').html(arguments[0]);
        return proxied.apply(this, arguments);
    };
})();

Answer 1

You are not modifying the open method inherited by XMLHttpRequest objects but just adding a method to the XMLHttpRequest constructor which is actually never used.

I tried this code in facebook and I was able to catch the requests:

(function() {
    var proxied = window.XMLHttpRequest.prototype.open;
    window.XMLHttpRequest.prototype.open = function() {
        console.log( arguments );
        return proxied.apply(this, [].slice.call(arguments));
    };
})();

/*
    ["POST", "/ajax/chat/buddy_list.php?__a=1", true]
    ["POST", "/ajax/apps/usage_update.php?__a=1", true]
    ["POST", "/ajax/chat/buddy_list.php?__a=1", true]
    ["POST", "/ajax/canvas_ticker.php?__a=1", true]
    ["POST", "/ajax/canvas_ticker.php?__a=1", true]
    ["POST", "/ajax/chat/buddy_list.php?__a=1", true]
*/

So yeah the open method needs to be added to XMLHttpRequest prototype (window.XMLHttpRequest.prototype) not XMLHttpRequest constructor (window.XMLHttpRequest)