How can I modify the XMLHttpRequest responsetext received by another function?

Question

I am trying to modify the responseText received by a function that I cannot modify. This function creates a XMLHttpRequest that I can attach to, but I have been unable to \"

Answer 1

One very simple workaround is to change the property descriptor for responseText itself

Object.defineProperty(wrapped, 'responseText', {
     writable: true
});

So, you can extend XMLHttpRequest like

(function(proxied) {
    XMLHttpRequest = function() {
        //cannot use apply directly since we want a 'new' version
        var wrapped = new(Function.prototype.bind.apply(proxied, arguments));

        Object.defineProperty(wrapped, 'responseText', {
            writable: true
        });

        return wrapped;
    };
})(XMLHttpRequest);

Demo